They are rubber cabinet bumpers I got off Amazon, used as properly located Mac homing dots.

Until they caved to PC convention, with the release of the original iMac, Apple had their indexing nibs on D and K, so I have kept adding my own, after they switched.
Indexing with the same fingers, everywhere, makes much more sense to me than indexing the alphas with my pointer fingers, and the numpad with my middle finger.