How about holding someone's gaze, then glance away, glance back to check they are still looking and then hold the gaze again. Maybe add a half sigh or a lip bite for good measure.

Apparently when women used to carry fans, there was a whole range of messages that could be communicated to a man by the way the fan was used. So if you see a woman with a fan, she might be flirting the old fashioned way.