Well, I'm Fester - completely bald and short. SNAP is another I've seen several places (Sensitive New Age Pilot). Waldo, cause you can never find the guy. Powder - bald and very pale complexion. Our FNG is Sling, from his habit of wearing these little bikini briefs (very disturbing thing to see in a crowded 8-man stateroom). Karen Hultgren, the first female F-14 pilot, later died in a crash off the Lincoln, was "Revlon" from showing up at the squadron after a photo shoot (for some "women of today" type magazine thing) still wearing the heavy makeup - see the book about her, "Callsign Revlon". My all time favorite is Fishnet, a guy in my RAG class who was so hairy (think Missing Link) he once caught a fish in his chest hair while swimming in Pensacola Bay. Maybe a b.s. story, but I talked to at least 3 guys who swear they were there when it happened.
Usually after you first get to a squadron, callsigns get bandied about by the j.o.s, trying to find one that fits. I find callsigns become "official" when you get called up to the front of the ready room for something and everybody yells it out, and/or, it's how the skipper starts referring to you.
As for the helmet thing, squadrons usually have a common scheme, though much less ornate than the ones in the movie, and your callsign is usually on the back, not the front, so you can find it on the rack in the paraloft.