Odd and Probably Unique Alarm
When I was a student, our club's trainer was N38290. The flight school on
the field had a trainer N3829Z. My CFI talked to the local FSDO, and they
agreed to waive the fee for changing the N-reg because of the potential
conflict with students in such similar registrations in the same pattern.
But the club refused because they didn't want to repaint the aircraft.
For local flying, one can apply for a special callsign.
For example, The Ohio State University Flight School aircraft all end in
OSU. Instead of hearing a constant "zero sierra uniform", the aircraft
have assigned numbers painted on the tail and use that number preceeded
by the callsign "Buckeye".
Now what one hears on the frequency is "Buckeye 35", "Buckeye 11", etc.