There is an occasional non game breaking bug in AI, where you sometimes come across a floating pistol. Here it is zoomed in. Amazing attention to detail.
Not nearly as much attention to detail, more of an Easter Egg, but I did notice this tattooed on BJ's arm when playing through Wolfenstein recently:
Alphabet code - reference to D O O M (4th, 15th etc letters) by the same id Software guys/loosely-connected game lore, but disguised as a concentration camp tattoo when BJ gets sent there.