Imagine having any card selected and signed and you then draw a black permanent dot on the back of the selected card and the spectator can feel it's dry and doesn't wipe off.
You then are able to drag that black marker dot to any location of the card several times in any direction you wish finally coming to a stop. You then reveal it's still there signed and selected card with the dot moved to a completely different location on your card!

Easy to do

The gimmick takes seconds to make once the materials are obtained

The selected card can be given away at the end as a souvenir

Very quick reset