-Check when they are voting. If they vote at the same time as somebody else, they could be in an alliance.
-If they are Very talkative/extremely silent
-If they are friends with someone in that game (check by looking at their friends list)
-Check previous games, and see if they did tributes to anybody
-Check recent blogs. (Some people try to hide tributes by doing them in a blog)
-If someone sends you a message saying alliance, 9/10 they are in an alliance with someone else.
-If one person seems to get positive comments a lot, it could be alliance members plussing them.
These are just a few things.
I hope these helped you!
