Ask them to try to rub away the X - they can't! It's Sharpie ink! Tell them not to worry though - it's safe and nontoxic and can be washed away easily with soap and water.
The secret behind Double Cross is diabolically clever, and perhaps more importantly, practical. It's always inked and ready to go. There is nothing you need to make or prepare beforehand - just throw the pen in your pocket and you can perform it all night long.
Because there are no difficult sleights, you'll sail through the routine. You're so far ahead, the spectators will never remember you coming near them or even touching them. The result is a unique magic effect that's self-contained, has NO reset, and can be performed surrounded. It's a table hopper's dream.
Double Cross includes the MagicSmith designed and fabricated Double Cross Sharpie pen, accessories and online instruction link.