Also used by the Winlink system on the ham bands. They should do a CW ID after the QSO, so that's why you heard what you did on 20m. They use other soundcard modes too, ARDOP and formerly Winmor (just "sunsetted" recently) VARA is favored at the moment due to it's speed. MARS had a parallel system of Winlink also, many of the MARS ops also do SHARES, so that can account for the non-ham sigs.