Don't know it to be necessary but fresh paint under the vinyl provides a clean, smooth surface. I usually paint it first or spray with an acrylic clear coat from a can. The clears dry very fast.
The bare wood needs to be sealed, as others have mentioned. My son owns a signage business and recommends further that you use a fast drying sealer/poly coat. The first coat will likely raise the wood grain and result in a not so smooth surface. Sand lightly with fine paper and re-coat. Lightly sand after final coat to eliminate dirt bumps and the last raised wood grains. Let the sealer dry/out-gas thoroughly to prevent bubbles later. Good luck.