Subtle flirting.............?

So, there's this girl that I think might have a little bit of a crush on me. She's about three or four years older than me and for certain reasons she can't openly flirt with me. I feel as though I am going to have to initiate the flirting, but I am going to have to be subtle about it. I'd rather not get into the details, but it's nothing morally wrong or taboo, we aren't related, neither of us are married, it could just cause a bit of a riff in our personal lives. Also, I could be reading her signs completely wrong. So, basically, my question is, how can I subtly flirt with a girl, where if she's interested she may start flirting back, but if not, it could just be taken as innocent conversation, or run of the mill actions?