Green’s Dictionary of Slang

marker n.1

[SE mark, to notice or observe, i.e. the shoplifter’s activity; to identify with a mark; note later mark v.]

1. [late 16C–early 17C] (UK Und.) that member of a pickpocketing or shoplifting team who takes the stolen item from the person who actually picks the pocket.

2. [1950s–70s] (US black) a person engaged in ritual teasing or mocking.

3. [1960s+] (US black) the bait that lures a victim into some form of swindle or other fraud.