I made all our paddle trail markers out of rough cut cypress, and I ended up picking up some artist’s paintbrushes and hand painting them. For smooth-surfaced pieces, I’d just paint first and sand after (with sanding sealer as a helpful pre-painting step, especially on open-pore wood), but I’ve never come up with a better way of adding color to unsanded rough cut stock.
Painstakingly hand painting the routed parts of the signs was quite tedious, and it was like playing Operation on steroids (as sanding off errors wasn’t possible), but I got the results I was wanting. Of course, for the several hundred 50mm/2" cypress magnets I’m making to give away at our table at Earth Day this year, I’m giving up the rustic look in the interest of production efficiency, but if anyone wants a rustic one, I will gladly make one for quite a reasonable price. 