There is a very good chance that he is just not used to making that next step to asking you out or he just doesn't know how to do it. I don't think there would be anything wrong with that. I think that if he is showing you signs and you are interested, then maybe you should take the initiative and ask him out. This is something very untraditional, but sometimes it saves you some time of waiting for the guy to make the first move. As for what signs to look for, well, all guys are different, and their signals are different.
Some guys even ignore women as a sign.
Hope this helps. I have liked a guy at work for about six months. At first it was okay considering that he did not know that I liked him. He later found out and was playing it for all it was worth. I told his friend that I was not about to play games if that was his intention.