Just watching the MASH episode where Hawkeye and Trapper were cited for "altering salute by placing thumb on nose."

When I was little, there were two ways to thumb your nose. Sticking your thumb on your nose and wiggling your fingers was a little naughty. The other way, where you put your thumb against your nose and then flicked it at someone, seemed to be more punishable. I don't know if it had a specific meaning, or if it's related to the stuff where you flick your thumb off your chin or teeth. My mom was Italian, so I guess it could be an Italian thing.