Every flarm display behaves differently. Some displays are more intelligent than others. So this explains the different in symbols.
As for call sign, you should see the contest number if the flarm or ADSb is registered on flarmnet.org. Yes you can and should register your ADSB on flarmnet if you don’t have flarm. Flarmnet converts your ICAO code to recognizable contest number. Both flarm and ADS-B transmits you’re ICAO code. I wish every pilot register their device on flarmnet. It takes 1 minute.

Ramy