Wrinkles should merely indicate where smiles have been.

The line reframes aging as a visible record of joy rather than decline. By suggesting that wrinkles “should” mark where smiles have been, it treats the body as an archive of lived experience—especially laughter, warmth, and sociability. The gentle moral pressure in “should” implies an ideal: a life oriented toward good humor and human connection will leave its traces, and those traces deserve pride rather than concealment. Often attributed to Twain because it matches his public persona as a humorist, the sentiment also fits a broader late-19th/early-20th-century tradition of aphorisms that valorize cheerfulness as a kind of character.