Many years ago, in a previous life, I heard about the ~friendly competition between Caltech's Dabney and Flemming houses. Various spacecraft components would have "DEI" (Dabney Eats It) or "FEIF" (Flemming Eats It Faster) hidden on them. But there's apparently nothing online about that. Or at least anything that's indexed.
Legends of Caltech, page 69 has the story and a photograph (looking at my copy right now). It was a valve package plate on the Voyagers ink-stamped with “DEI/FEIF”.
Anyone?