these are lovely! props for hand drawing the signs instead of cribbing a pretty font off the web.
personally i would get something like this:
which can handle various paints and spray consistently. worst case scenario, you could experiment with adding a little water to a water-based paint to thin it out, then spray on multiple coats as they dry with the occasional sanding.
you could simply spray lighter and sand all over for each coat but i think that sounds like too much work. it’s easy to do on large surfaces, but it would probably be a pain on this sign (although you could do a two-tone finish and paint the edges a different color; something like black would probably hide any imperfections there and the face is easy to sand).