Is there any way to tell if a girl is trying to flirt, or just be friendly?

I'm just curious, because I literally have zero experience with women. But, over the last couple of weeks, there have been two times where two random girls I met in passing gave me subtle little compliments. I didn't think much of either instance, but it's kind of bizarre, because I can't recall a time where a girl has ever given me any kind of attention that she didn't have to, let alone to have it happen twice in two weeks.

It's not like anything about me has changed, either. I still look the same, dress the same, act the same, etc., as I always have. So... is it just a coincidence that two girls happened to be a little extra friendly, or is there something I'm missing...?

What were the compliments?

Well, with the first one, I don't know if "compliment" is quite the right word, but the only one I could think of. Basically, I tend to wear shirts with goofy sayings and whatnot, to see if anyone ever notices. Nobody ever does; I guess this first girl kinda got a kick out of the one I was wearing. With the second girl, I can't actually remember what she said. @_@ Probably just my imagination making something out of people just being friendly, but still, like I said, that never happens to me, so it just struck me as odd, is all.

So you were saying they were just comments about your tshirt. Then it's just random comments then, nothing unusual about that......means nothing. If the same girl makes a comment again, then there might be something there to pursue.