Actually, MDO might be less expensive and better.

Marine grade plywood is designated as such simply because it is manufactured with no interior voids. Some brands may have binders with better weather resistance than others.

If you wish to have a design/name etched/routered into the wood, then a solid wood such as cypress or Ipe would be a better long term choice. Those woods---plus cedar, white oak, ash, and even several species of mahoghany(all of which don't look as smooth when painted)---all have some degree of natural weather resistance.

We get MDO ply with paper smooth surfaces for making signs. You can get it with paper on one or both sides. It costs about $70 per 4x8 sheet.

We paint all edges and both sides with exterior primer and paint before putting on the sign letters or logo. The sign will fade or peel before the wood deteriorates.