(Yea we know it's corny)
Borrow a dollar from a spectator, have them sign it and place it in an envelope. Now, Pull the Hot Stuff Lighter from your pocket and hand it to the spectator. Hold this a minute!, you tell her. Seal the envelope, and hold it over the spectator's lap. Ask the spectator to use the lighter and burn the envelope to ashes, along with their dollar. Take the lighter back put it in your pocket and exclaim Well, that didn't work like I thought!
Begin another trick, pause and say Ouch! That lighter is gettin' a little hot!
Now pull the lighter apart and give them back their signed money!