I think Mia'Cova could tell by my body language and by my demeanor when we first met. He led me carefully that first day. I have a difficult time meeting people's eyes when I speak with them, but not necessarily because it is a submissive trait, but beause it feels so intimate. After about 1/2 an hour I was gazing into his eyes, even though I was nervous at first.
He would ask me leading questions, "Do you want to do this?" and "Is this ok to do?" and see my reactions. He wasn't really asking for permission, so much as GIVING me permission to want those things... if you see what I mean.
*sigh*
I'm not explaining myself very well and I don't think I've helped. LOL Perhaps he can explain how he knew I was his sub better than I can.