What message is she trying to send?

Everyday when I go to work, I always see a girls who normally gets on the same train(the tube) as me. I say normally as I always have to make a connection half way through my journey. I don't know her as we're just strangers, and the "etiquette" on the tube is not to speak to others.

We both always catch each other looking at one another and we both look away knowing that's they caught either of us looking at them. One time she got on a train that didn't even go to where she was going that I was on and got off later on but I saw that she was looking at me at one glance. Today I saw her waiting at the platform and we both looked at one another and then looked away, I looked again just to give her a smile but didn't as she was looking to her right glaring downwards. I might of thought that I might of done something wrong, so just played around on my IPhone.

I'm useless when it comes to this stuff as I have never had a date before, so I can't really tell if someone is interested in me. I wouldn't be surprised if she didn't like me though but it would be a boost of confidence if it is a sign. Also what would you do if you were in my situation?

Don't wait around just talk to her maybe she's looking for your attention.
She probably wants you to talk to her and she wants to talk to you too.stop waiting around and just go for it you have nothing o loose.

What would I do if I was in your situation and stop second guessing if she liked or what? I'd go up and start a conversation with her!

The smiling back thing was right it was a shame she was trying so hard not to look back at you, like everyone else has said Talk To Her maybe say something like "I see you everyday on the tube and I still don't know your name I'm (whatever your name is)"