If he makes an effort to say hello?

If a guy makes an effort to say hello and goodbye to you, how can you tell the difference between being friendly and being interested?

My dilemma is that this guy always seems to make an effort to say hello and call my name even when I am not in talking distance, but rather shouting distance lol. I also caught him staring at me. He doesn't seem like this with his other friends, but for other girls out there that are trying to decode this, if there are any, what can you suggest?

I just want a sign that will give me the go-ahead to flirt with him but not come on like a weirdo :P
If he makes an effort to say hello?
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