I made friends with a bunch of girls this year. I noticed when I am sitting there they come over place their hand on my upper back, say hi etc and leave it there for a bit. Similarly if They are sitting with me and leave they do it again. or if they are far away they smile and or wave to me.
Thanks for the answers. The girls I have noticed doing it are the socially outoging one but they don't seem this comfterable with other guys. There is one girl I have been meaning to ask out and would feel really bad if I gave these girls the wrong idea.