Borrow a pen, write with it, and then casually remove your hand, while the pen remains standing unsupported.
This is best performed as an off-beat effect where folks do not expect a trick, but the magic just happens. The pen is unprepared. The notebook hides the gimmick which is for all practical purposes invisible.
Bonus routine is a rubber band ring linking effect. A borrowed ring is linked into two rubber bands. This can be performed impromptu.
1st edition 2018, length 40 min