We frequently use stamps in our work. There are many commercial stamps available to buy that are fine to use in your work. There are also quite a few that are not, so be sure to carefully check each maker's angel policies and copyright information. We personally feel that one way to preserve our personal style is to create stamps ourselves or trade one-offs with other artists.
To make stamps, you'll need some scrap clay, not too wet. All sorts of tools can be used to carve