There's a standing tradition, at least in the USA, that a student pilot has their shirt cut, signed and dated by their instructor. What is the origin of this practice and what is its significance?
Supposedly, this is because in the early days of flight before intercoms were common instructors used to sit behind their students in a tandem aircraft and pull on their shirt tails to give directions. After successfully soloing, the student has shown that he doesn't need that direction any more and therefore doesn't need his shirt in one piece either.
This isn't a universal tradition: I had the end of my tie cut off to mark my first solo (in South Africa). I had to go out and buy a tie first!
As a young pup hanging around the city's airport, this seemed quite the oddity. Seeking council from a very senior pilot, he acknowledged the following details concerning the habit of cutting off a solo student pilot's shirt tail. "Back in the days of the barnstormers, the aircraft of the time (Jennys, mostly), did not have all the modern electronics that we have today. Most importantly, the radio was not yet available in aviation. So when a flight instructor felt that a student's airmanship was solid enough (would not reasonably crash the aircraft), it became incumbent upon the instructor to tie a rag on the aircraft, sometimes the tail wheel or wing struts of the aircraft, as a visual method to WARN other pilots that THIS aircraft was being flown by a student pilot... someone who was VERY inexperienced in the art of flying by himself, and to give him wide berth. As such, finding a rag on the open airfield to be used for such purposes was a rarity. So? The instructing pilot would whip out his pocketknife and cut of the tail of his flying pupil's shirt which would then be attached to the aircraft." His explanation made perfect sense... thought I'd pass it along.
Several traditions have developed in the USA around "soloing", including drenching the student with water and cutting off and permanently displaying the back of his or her shirt.
In American aviation lore, the traditional removal of a new pilot's shirt tail is a sign of the instructor's new confidence in his student after successful completion of the first solo flight. In the days of tandem trainers, the student sat in the front seat, with the instructor behind. As there were often no radios in these early days of aviation, the instructor would tug on the student pilot's shirttail to get his attention, and then yell in his ear. A successful first solo flight is an indication that the student can fly without the instructor ("instructor-less" flight). Hence, there is no longer a need for the shirt tail, and it is cut off by the (often) proud instructor, and sometimes displayed as a trophy.