My first VATSIM experience

I’noticed som VATSIM users are able to insert ‘airline’ in their VATSIM datastring , i.e.they are able to send their flightname,for instance : Topswiss, Easy, Rednose,Speedbird. I’m able to view this by using littlenavmap(you must be vatsimconnected to be able to view this feature). I can’t figure out who this ‘airline string’ is made ! I’m only able to send ‘registration’ ie SAS344 when sending flightplans. Tips are appreciated …