tits on a keyboard
Small bumps on certain keycaps to help touch-typists find the home keys (ASDF and JKL;) without looking. They are found on the "F" and "J" of a QWERTY and the "5" of a numeric keypad. The Macintosh, perverse as usual, has, or had, them on the "D" and "K" keys.
This term is based on the vernacular American expression "as useful as tits on a boar" (or boar-hog, bull, bullfrog, or many other variants), meaning "not useful".