Sometimes we think they like us, we feel like a woman likes us, but for whatever reason we are still not confident in our diagnosis. There are things we can do simply to test the water and find out how comfortable or attracted to you they truly are. So what can you do to test the waters without impeding on them? You use covert techniques that are normal, but still send tells and give a reaction.
Brush up against her (neutral guys, shoulder to shoulder not intimate areas), observe her reaction to your action. A lot of times if we are attracted to someone and they run into us we flirt back, in other words, we reciprocate. However, whenever we feel they are creepy or unattractive we lean away, even step back. How welcome is that slight touch? If it is welcome and they are comfortable you are certainly standing on decent ground.
Impede on her space, step into her intimate zone and again observe her reaction. When someone we aren’t attracted to steps in our space we step back. When it is our friend we give them a more space, leaving them in the social zone, 4-6 feet which sounds like a lot and also depends quite a bit on environment. Obviously in some environments it is impossible to give people their space (crowded areas). The intimate zone is 2 feet down to touch; this is especially reserved for women we are attracted to. Often times we can impede on this space by simply walking up and standing beside them, something that is far less threatening.
Talk to her softly, this is an awesome tactic. I use this quite frequently and it works in closing the distance logically and finding out how attracted they are to you. A woman will lean in when she is attracted to a man and find out what he is saying; after all she is interested in him, which often means interested in anything he has to say. She will lean in because she wants to hear what you have to say.
These tactics are simple and more importantly natural, things we do to people on accident all the time. If an attraction is obvious these tactics even allow for a slight escalation, because after all they are a slight escalation. You are closing the space, adding touch, and having them close the space. Use these techniques with caution, if someone is obviously uncomfortable with you, this will just turn them off further.