Just bought another A319 for my Toronto-based airline. The assigned registration is C-ABBA. All my A-319/321s are named after Canadian cities, so C-ABBA had to become "City of Waterloo".
My CRJs are named after famous Canadians and my 787s after Canadian rivers or lakes.
Used to run an airline in Russia and named all the aircraft after Russian Cosmonauts. Spent a *lot* of (good) educational time on Wikipedia because of this :) .
Nowadays, I prefer to label (in the "Note" field) the routes of all my aircraft (e.g. VIE / FRA / PRN / STR*, where the * points out an irregular - non daily - schedule) - similar as to what Matth has posted earlier in this thread.
I name my planes. Sometimes it's a joke with my friends, or a joke about the cities it serves, but mostly I let my friends on Snapchat and Instagram name them. As of now I have
Billy Jean
Buckwheat
Sassafras
Bubba
Fella'
Cletus the Fetus
Dr. PumpeeMonkee
SarBear
What is Cuda
Real Riverside Sh*tshow Express (mate if this breaks rules tell me)
They don't have any meaning. In the personal notes I put the aircraft's base airport. I have 9 at DAL and 1 at ONT.
I used to do that with a smaller start-up in temporary game worlds. It's manageable for a 100-aircraft fleet. But now I have over 1100, what I do is to number them by certain rules. E.g. Boeing 737-8Max, block 1, the code for the block is M, so 3MA,3MB,3MC...
My personal little interest is to label the special mark of the fleet and then I'll name them. E.g. 1st aircraft: Enterprise; Since this game is all about being happy achieving the dreamed airline world, I had a special livery fleet.