A love token on an 1891 seated liberty dime bearing the letter M which I recently purchased at auction.
Love tokens were popular in the United States from circa 1860 - 1910. An individual would smooth one side of a coin and engrave initials, words or symbols of personal significance. In the American tradition, the love token was given to a sweetheart as a token to be carried at all times.
A more detailed history of love tokens is available at the PCGS website: