This is exactly what this thread is about 
Asobo: Please can you add the ability for injected SimConnect aircraft show labels.
At the moment, injected SimConnect aircraft do NOT show labels, so any Injected Plane is very hard to spot when flying … compared with the non-injected Aircraft.
Hopefully, adding this Label ability, that is already available for non-injected Aircraft, is not a major development task, and was probably just an oversight .
The lack of these labels is a particular issue, with Apps that inject or read by Simconnect aircraft, in MSFS, ie Vatsim / IVAO / LNM . / JoinFS