The easiest and simplest finish is oil. Get some boiled linseed oil and just rub it on with a rag. Wait a day, and repeat. You can add a small amount of stain to the oil if you want to go darker. Test plain oil on the surface of the stock before you cut it to see what it'll look like. This is just about the most foolproof finish, and you can add more coats anytime, and rub with fine steel wool to get a nice shine.

Luke

Edit to add: It occurred to me that I had assumed this would be an indoor sign. If it's going outdoors, then oil probably isn't the best choice. In that case, I'd use spar urethane or paint. Either one of those requires some technique to do well, though.