Here's my thoughts. Players can be easy to spot but not always, there is no rule. Your best bet is that if you decide to put out for a guy just make sure hes a nice enough guy that you wont feel bad if it turns out he was just physically attracted to you, since sex in itself doesn't make a guy a player, its his attitude towards women which do. A nice guy will still keep you around even if you two don't work out, or will at least be open to ideas of dating and getting to know you better in many cases.
Physical contact is one, but watch how the guy is with other girls. Some guys constantly put their hands on everyone, so that diminishes the significance of physical contact with you in particular.
Compliments of any nature are a sure sign, guys don't often think about things like purses, dresses, hair, shoes, or accessories, if hes pointing them out to you hes trying to say "I notice you, and I like your style". A key one is hair, if you do something different, change the color, or whatever, its something most men wont notice unless they are into you, and certainly wont mention unless they are definitely into you (in my opinion).
Friendliness is things like "how are you today?" or conversations about anything mundane. Watch for anything that crosses over into the personal (beyond what you do for school or work) things like "and what do you want to do with your degree" they are probing your ambition and sense of purpose in life. Any inquiry into your interests and tastes means hes trying to find a common ground with you to begin and continue conversation, and means he cares what your into.
Finally flirtation is an obvious one. This might include poking fun at you or teasing, throwing things in your direction, any kind of game/play. Hes trying to see if you will engage him back. Some feel that flirtation is a sign of childishness but I find that when done in the right way its just another way to show obvious interest, it becomes childish when its the only way a guy can interact with a girl and when its overused in my opinion.