You mean like two-way eye contact? I'm pretty sure you can still read that stuff just looking at the back of their head. Other than that I feel like it was mentioned at some point that you can read class skills once you know their class and personal skills once you see them used but I can't find it properly explained anywhere on the wiki. I don't remember any good examples besides when it comes up in relation to concealing abilities like Lancelot's smoke or Mordred's helmet, so however you want to run it is probably fine. 

EDIT: [url=http://typemoon.wikia.com/wiki/Secret_of_Pedigree]Secret of Pedigree[/url] implies some stuff about how it works, but makes it seem like the norm is way too transparent.