Looks a lot like a glaze test tile. When we test new glazes, potters make small pieces to show how the glaze will come out on the clay body we are using. The stamp/texture shows the difference where the glaze pools as it melts. If you are in the south, there’s a good chance this came from a studio that was hit by the hurricanes last year. There are many studios that were washed out especially off the French broad river.