SBS doesn't output heading either (only track), but in this case said C-37 doesn't broadcast track (although of course it's possible to derive average track from successive lat/lon reports).
In this case I was not using mlat and the bearing was shown in PP under 'course', so I assume the ac was sending it.
To clarify, that C-37 sends ADS-B Airborne Position squitters (which is why it plots on BaseStation) but doesn't send ADS-B Airborne Velocity squitters (hence no groundspeed or track on BaseStation).
It
may send track and/or heading as EHS DAPs, but none of the enthusiast Mode S receivers decode these, so the PP course value can only have been derived from successive ADS-B position reports.