Ya obviously that's the key indicator but that's only if they shoot back
Say if you're initiating with said gang and everyone has tags and you wipe them, then you get some guy named "PacketLoss.AHK" coming up after and you don't know if you're initiated because who knows he could just be an innocent bystander or he could be with the gang you just wiped. Either way, he doesn't have the tag forcing you to either not shoot, re-initiate or take the shot and risk the RDM ban
Bottom line is that it's a very simple rule which requires no coding on the devs behalf