my master told me he could tell I was a submissive(when I was 14) because I wore this slave collar and I let any dominant/controlling guy pull me around by the leash, and if a girl who wasnt as controlling wanted to I wouldnt let her. he also said it was by the way I acted towrds controlling people, I never looked them in the eyes,I alwaysw bent my hea down when talking to them ect.

basically you can tell by body language