Similar story to FedEx727's post:
RAF Waddington about 10 years ago. Watched a member of the public taking a rubbing/impression of the numbers and text from a man hole cover. When I asked him why, he said that military establishments often had quite old and rare examples of the things, because they don't get replaced as often as those out there in "the real world". Wasn't sure what to make of this unique pastime of his, so decided to return to the beer tent to carry on with mine!
Also flew with a chap on the E3 who would come up to the flightdeck during AAR to get the tail number of the tanker. We'd ask the boom operator for their number and he would make a note of it. Still had to see the aircraft with his own eyes or it didn't count apparently. The boomer (sp?) would often query why we had asked for his tail number, as that wasn't the norm. Never knew how to explain it without sounding too daft. This chap would take serious banter from the rest of the crew but just didn't care. Water off a ducks back. Good for him.