I don't think there is a difference between kisses. It's just a sign of affection...but if you want to analyze it, here it goes:
Kiss on forehead: Brotherly, I'll-watch-out-for-you kiss
Kiss on cheeks: I think you're cute and I would date you
Kiss on lips: Let's date or let's hook up
Kiss on neck: I'm horny and I want you to be too
Kiss on top of head: Same as forehead
Kiss on hand: Trying to be classy but don't know how to be classy
Kiss on nose: Wtf?