Here are some basic template shapes I drafted for making stamps which can be used with ink or paint onto surfaces like paper. You can also make stamps to use on clay, dirt, slime, putty, or other materials. You can put any image onto the stamp bottom to make an imprint. I am personally making stamps for pottery vessels.
Bring these sculptures into blender and then put any kind of high relief shape onto the flat square bottom. Then bring it into a slicer and print it using a 3D printer in any size you would like. Remember to wash ink and paint off of stamps right away if you are not coating the base of your print in rubber after you make it.

I am putting together an instructable to help show what drafting solutions I've found to put any computer image onto the stamp.
Completely free to use. Please don't sell the base, but feel free to create a stamp and then sell that stamp. I hope this is helpful!