April (@coffeebean) made one out of lasered acrylic and demonstrates its use in ceramic work here:
@nicksilva makes tons! of leather embossers, usually out of delrin, I do believe, e.g. this one where he discloses a less-than-perfect experience
and here’s one that worked well
As Kevin says, using something like Fusion 360 and doing as much “parametric” as possible will make it so you can test several methods and media and make adjustments if needed, being that, for example, a stamp for ceramics might differ a fair bit from “the same” stamp for “branding” leather, the latter necessarily needing to be capable of being heated to much higher temperatures…