The M on your palm is not rare, and the pages calling it lucky or a sign of money point to no old book. It is the shape your heart, head and life lines make together, and most hands have all three. Hold your hand sideways and relax it to see yours.
Almost every page that ranks for this tells you the M makes you rare and destined for money. I searched 41 old palmistry books for the letter M. The passages those claims would need are not in them. This is for fun, not fortune.
How the M shape forms
Hold your palm open under a lamp. The three biggest creases are the heart line near the top, the head line below it, and the life line that curves around the thumb. Together they can look like a letter M.
Frith and Heron-Allen give a trick for seeing it. Tilt your hand sideways and relax it:
"These three lines form a figure in the palm of the hand something like the letter M ; if the hand be held sideways and with the muscles relaxed, the figure will readily be perceived."
So the M depends on how you hold your hand. Held flat and stiff, you may not see a letter at all. If you would like to see which of your lines the old authors would name, you can read your own hand with Alma. It is free, with no sign-up.
Carl Louis Perin, writing in 1902, also counts three:
"The three most important lines in the palm form a large letter M, each line of course having a distinct signification."
He puts the life line first, and it is the one that wraps the fleshy pad at the base of your thumb, the Mount of Venus:
"The Line of Life extends from the base of the Mount of Jupiter, around the Mount of Venus; in the left hand it forms the first branch of the letter M."
He is just as plain about the second stroke. The head line, he says, is the one that runs parallel to the heart line:
"The Line of Head is the main line running parallel to the Line of Heart, and in both hands forms the second branch of the letter M."
That is where I take the advice to look at both hands. The life line is described for the left hand, the head line for both.
How common an M on your palm is
Very common. The M is what you get when the three main lines are all there, and on most hands they are.
Frith and Heron-Allen say these lines are present in "the majority of hands":
"There are three or four very important lines observable in the majority of hands."
William Benham's 1900 manual gives a number for one of them:
"The Head line is present in ninety-nine per cent, of hands, though sometimes very short."
He says the heart line is a little less secure, and the life line is seldom missing:
"The Heart line is seldom absent, though more often so than the lines of Head and Life."
No book gives a percentage for the M itself, so I will not make one up. What the sources support is simple: if you have the three lines, you have the pieces of an M. How clear the letter looks depends on how deep each line is and how you hold your hand.
What if you have a strong fate line
The fate line is the upright line that runs up the middle of the palm. The four-line pages put it in the middle of the M. The two books that describe the letter do not. Cheiro describes it like this in 1897:
"The line of fate (Plate XIII.), otherwise called the line of destiny, or the Saturnian, is the center upright line on the palm of the hand."
So a strong one is a separate feature, and the books do not fold it into the M. Cheiro even warns readers against making too much of a strong one:
"an apparently very strong line of fate on a conic hand, one must remember that it has not half the importance of a similiar line on a square type as far as worldly success is concerned"
The M is the three lines, and the fate line is something you look at on its own.
Why most pages count four lines and these books count three
Many pages online build the M from four lines, add the fate line, and then call the result rare. The two books that lay out the letter stroke by stroke use three: Frith and Heron-Allen in 1883, and Perin in 1902. With three lines that most hands have, "rare" stops making sense.
The one author who read it as a warning
Three authors named the letter: Frith and Heron-Allen, Perin, and J. J. Spark. The first two are just describing a layout. Spark, in 1900, does something different. He writes about the letter turned the other way round:
"When the Life, Head and Heart lines are joined together forming something like a capital M written backwards"
He says the judgment of that hand is "dominated by the animal impulses", and then he predicts disaster for the whole life. I am not printing the rest. It was never true, and a line pattern on your hand cannot show it.
So on this one question, the books split. Frith and Heron-Allen and Perin treat the M as a map of three lines. Spark treats a joined-up version as an omen. They are not even describing quite the same shape.
Where the luck and doom claims come from
I could not trace the money and good luck claim to any book in the library. Not one passage ties the letter M to wealth, rarity or fortune, and I have no earlier source to point you to, so I will not guess at one. What the old books do have is promises and threats pinned to the heart, head and life lines one at a time.
Here is why that matters. Benham said the quiet part out loud, writing about another line, the sun line:
"Palmists who have a pleasant story to tell, get the most clients, and this being known to professionals, leads to a system of flattery totally out of proportion to the subject."
An M that "means" something gets people to book a reading. The sun line page has more on that quote.
What Cheiro said about it
Nothing, as far as I can find. I searched the library for Cheiro and the letter M in several ways, and none of his books in the library has a passage that names an M on the palm. He wrote a lot about each of the three lines separately. He never gave their combined shape a meaning.
So if you have read that Cheiro explained the M, the books I have do not back that up.
What each line was said to mean
Each line has its own page and its own claims, so here is the short version. The authors do not agree on which stroke of the M matters most. Cheiro gave the head line top rank, and Edward Heron-Allen answered, "of course", with the life line:
"In all my work I regard the Line of Head (page 11) or the Line of Mentality as the most important sign that can be found in the hand."
"The most important line in the hand is, of course, the Line of Life (a a in Plate II.), which surrounds the mount of Venus."
If a page tells you which line of the M matters most, it is picking a side in a fight that never ended. Read more on the heart line and head line pages.
Where you see variants
A few related patterns come up when people compare their hands.
The first is a joined head and heart line. If your head and heart lines merge into one, the M loses its middle stroke. The books read this in more than one way. Ida Ellis, in 1898, reads it as emotion beating out thought:
"Head and Heart line in one=Heart has too much control over the head, causing a strong emotional nature."
Further on in the same book, her list reads the same formation as selfishness. Mrs. A. Robinson, in 1911, will not pick one. She says a single line on both hands suggests either too much head or too much heart:
"it would be a sign that by nature the subject had either too much head or too much heart"
The second is an extra line above the M. The Girdle of Venus is a curved line that sits above the heart line. Cheiro's 1900 guide places it like this:
"The Girdle of Venus, found above the Line of Heart and generally encircling the Mounts of Saturn and the Sun"
If you see an arc over your M, that is probably it. There is a longer note on the Girdle of Venus page.
Questions people ask
Is an M on the palm rare?
No. It forms from the heart, head and life lines, and the books say those lines are present in most hands. Benham put the head line at ninety-nine per cent of hands.
Does an M on the palm mean money or good luck?
I could not find that claim in any of my 41 books. The authors who mention the letter M only describe the shape or, in Spark's case, read a backwards version as a warning. I could not trace where the luck and money meanings came from, but it was not these books.
Which hand should I look at?
Both, held sideways and relaxed. Perin says the head line "in both hands forms the second branch of the letter M".
Why do I not see an M at all?
Probably because of how you are holding your hand, or because one of the three lines is faint. The heart line, Benham says, is the one most often missing of the three.
Read your own hand
If you want to see how your three lines sit, and what each of the old authors said about them, you can read your own hand with Alma. It is free, with no sign-up. You take a photo of your palm and I point out the lines I can see, quote the books that mention them, and show you where those books disagreed.