Well Im not sure about how you can tell if a woman is taken, but I do know how to tell if a man is.
Fat
Smokes
Looks Depressed
Carrying a Six Pack of Beer
Wearing a Wife Beater T Shirt at the Beach
Driving a MiniVan
Sitting on a Bench Outside of Victoria Secret
Eating a Cooked Turkey Leg while shopping at Wal Mart
Says "Titmouse" or "Pussy Willow" without snickering like a school girl.
Ok if you can circle 3 of these he is DEFINANATLY taken.
For all you single ladies out there I just made this as a quick reference guide. Oh and if you want to know I circled all but the MIniVan or me.