I believe bulls have a natural instinct to spot cock craving wives in a social environment, but I don't think they are necessary able to identify a cuck husband at least initially.
The wife is usually the one who shows the first signs, the way she retains eye-contact, and how she accepts their flirt on hubby's presence. Alpha males and especially black guys are not afraid to test the waters and push the boundaries. They're natural-born "players" willing to do anything to smash white booty, regardless if it happens with hubby's blessings on not!
However, when a BBC is openly flirting a wife, a hubby's behaviour can be indicative whether it's cuckold relatioship dynamic that requires hubby's involvement or just another narrow-minded hubby who just can't see it coming.