As well as fixed frequency tones and sweeps the chirpy part (which sounds like a dial-up modem) contains data that the receiving machine can decode - you can put the name of the station or even a short message there. There may be some standard convention for what you should put there, though.
It's a Lindos test from a machine of this type: http://www.lindos.co.uk/la100oldl.jpg
As well as fixed frequency tones and sweeps the chirpy part (which sounds like a dial-up modem) contains data that the receiving machine can decode - you can put the name of the station or even a short message there. There may be some standard convention for what you should put there, though.
That was recorded off an analogue radio set, not digital.