I've tried bisque stamps, I've had some success with rubber stamps if I spray with WD-40 first, and metal stamps don't seem to be cut deep enough to get a good image.
So I'm trying my hand with wooden stamps. But I really don't like the wooden stamps commonly found in the pottery supply stores. I find them to be too abstract, too big to work on the curves of a mug, or just ugly designs.
So here's my little plug for the day. I've found Catfluff on Artfire and she's bringing over some wonderful stamps from India that work really well.
The designs are like those you would find in a Mehndi or henna design book. I think they might originally be made for applying henna, I'm not sure about that. They are abstract, yet have design to them. A very nice balance. And the wood is cut deeply enough to make deep impressions that I'm hoping will be visible after the glaze application.
I'm finding that the finger shaped stamps are great for borders and handles. They are thin enough to be visible inside of a curve but wide enough to really make an impact.
Over the course of an hour, I used this single stamp over and over again. I started with the very wet handles and then moved on to the slightly too hard leatherhard mug body. At no point did the stamp stick.
The wood is porous enough to absorb a touch of the moisture so the physics of the wood on clay make a natural release agent. And the cuts are deep enough that the moisture evaporates almost immediately so the stamp doesn't get waterlogged as you continue to stamp. It's just the balance I've been looking for.
Here are the stamps I've purchased (so far) but I've only played with one. And I'm very happy with that one.