The only thing they need is to either have a matching eye color, or the human needs a symbol of their teacher on their skin, because that shows there is a bond and no one else can steal the human!
I would suggest you give the human a similar theme to their teacher (colors, ornaments, cultural aspects, the works), so it’s easy to identify them as a pair, and it makes designing them together more fun!
If anyone draws their summoners please show them to me I get a kick out of seeing that stuff!
(And, I have some plans in place for a forum! I just gotta find some people who can help me organize it as I know from past experience it takes a lot of time and effort to get a community running smoothly!)