I found out you can put the spar urethane over painted wood, provided the paint is dried well. Thats for either oil or water based. These painted and clear coated pieces will get glued to the cedar backing that has the waterseal on it. Yes the adhesive will still adhere to the cedar as I tested it first, plus I am also using brad nails.
I asked the other question about putting the spar urethane over the waterseal because I was thinking about putting the sign all together and coating with spar urethane all at once. Instead, I coated all of the painted parts first because I dont know how the spar urethane will react to the waterseal, if it will work good or peel off in a short time. 2 separate questions for 2 different things. I will do a test board here for future reference so I know. Being my first time doing this, I had no idea what works with what.