Oramask is a stencil film that is really great with glass and metal etching, perfect for your wood signs as well.
It's sticky enough that will stick to your base coat, but when you pull it off, it won't lift up your paint or splinter your wood underneath.
It is translucent. You can see thru. This will make your work easier by being able to reposition easily, and being able to see if the edges are sealed properly, this will prevent from bleeding.