Cling stamps
From Craft Wiki
Cling stamps are rubber stamps that have a slightly sticky backside. This means you can mount the stamps onto acrylic blocks or a stamping tool.
How to use cling stamps
You can use cling stamps both with an acrylic block or with a stamping tool.
Positioning
Since you can't see through cling stamps, positioning them might be tricky. If you mount your stamp onto an acrylic block, you can use an L-shaped stamp positioner.
Another way to get good positioning with cling stamps is by using a piece of acetate in your stamping tool.