When I was learning we had a company callsign and a Number...like speedbird 22 but not as flash, when we were solo student we added a "Sierra" to the end...ie...Speedbird 22 Sierra.
I think that was an arragement with the on-site ATC and don't think it gave me any special treatment when talking to others.
Small point of note, I've never flown using a G-XYZQ callsign, always a company one. It's easier when you hear the company name, your ears prick up, is it the same when using G-XY...?