Street Slang
Several years ago an especially inept burglar plied his trade in Loudoun County, Va. While he was at work one night in an empty house, he was seized by a universal concern. He wondered what the future held for him. So he picked up a telephone, called a psychic on a 900-number -- and used his real name in making an appointment.
The Washington Post reported: "When the homeowner found the charge on his telephone bill and alerted the sheriff, the psychic gave up the suspect's name, dropping a dime on him even though he'd had a $250 reading."
The lady had dropped a dime on him. The Random House Dictionary of American Slang dates the usage from 1966. To drop a dime is "to inform on someone by making a telephone call to police; to inform or betray; to fink, tell, crack on, squeal."
Soon, I suppose, she'll have to drop a dollar on him... or somesuch.