How can I indicate my sexual interest in a girl subtly enough to to where if she doesn't reciprocate, I am not obliterated and falling flat on my face.

How do I subtly flirt? So that I have plausible deniability if I get rejected.

Too many times in my past have I outright told girls that I come across in my daily life that I'm interested, and then I fall flat on my face, and it's humiliating and sad.