When you're on a bus and people are going about their daily lives you are subject to more of a "day game." Because of this you are going to want to go with a more direct approach. The reason for this is because you two have some very real time constraints of having to do things, and the time when you guys get off the bus.
If you were to go indirect it gets a little weird doing opinion openers and stuff on a bus. You are beating around the bush without a lot of time to go through the 30 minutes it takes from going indirect and not showing interest to showing interest, and building comfort. Woooh! Thats a lot.
We need to go in direct here. She is going to have to somewhat judge a book by it's cover because she won't have the chance to see you interacting with others first, and she doesn't know about you.
You can simply do this by saying, "I noticed you over here and I wanted to come talk to you and see what you are about. I'm xxxx."
You're either in or you're out. You get on the bus you see her and you approach immediately. The longer you wait the creepier things get. Having balls here is what is going to spark some attraction immediately!
Hope it helps! Just smile, be confident, enthuisiastic...and get the girl!
Let us know how it works out