Hey Sherlock03.
It's often common for us to not pick up on when a woman is flirting.
I usually find a tell-tale sign of when a woman flirts with me, is flirting with me, is the unusual candid nature, sudden interest, and willingness to talk about anything, and everything really, often leaning towards racier content.
Because I tend to be so candid and honest in nature about things (and sometimes excessive), I often get accused for flirting with the opposite sex.
So now, at times, I even go to some lengths of saying that I'm gay (indirectly of course), because nine times out of ten, the girls that I just want a friendly, polite conversation with, think that I'm after more.
I'm not saying you should do the same if you come across as flirty though.
Oh dear, I've gone off on a tangent again, nevermind, hope this helps nonetheless mate.