Analogous to jail-bait only the person in question is married instead of under-age. Often-times they will act single and flirt with you, even possibly getting your number. He or she will never wear a wedding ring. You think you may be scoring, but watch out!
Victim: "That guy has been really flirting with me, I hope he actually uses my number."
Friend: "You know he's married, right?"
Victim: "What?! Why doesn't he wear his ring?! Man, I hate adultery-bait!"