Stamp

For the stamp bed TPU 95A works fine. Depending on the material and printer support might be needed (or bridging). To alter the text I added the Fusion360 model.

In the Fusion360 file is a modifier “surface offset” (last in the timeline) that can be used to add some tolerance between the TPU part and the stamp (default is 0.25mm). That might be too much depending on the accuracy of your printer (Thanks to MartinD for your feedback). Remove or supress the modifier in case you do not need tolerance between these parts or use some tape to tighten it.

UPDATE:

I've added a Stamp_V2 version that handles most of the issues reported to me:

• There is now a border around the stamp that gives some extra hold for the insert (looks better, too…)
• Added a screw hole for a 4x30 screw to improve stability
• Added a crease fold to the insert for easy insertion
• Added “declined”, “approved” and an empty version of the insert
• Added two holes to the insert for easy removal