You might try a method I have found effective in removing painted letters from an Awlgrip painted hull surface. I applied thick coat of Peel Away Marine Safety Strip to the painted letters using a paint brush and waited 24 hours. Most of the residue was removable using a plastic razor blade and the painted hull surface was not affected; this agent is water soluble and I doubt it would hurt the PVC . I then used Fromby's Furniture Refinisher with a white Formbys pad to remove all the residue but I expect that part of my approach could be detrimental to the PVC; you could wait longer than 24 hours or maybe a second coat of Peel Away would be better for you.
These are products I just happen to have on hand after years of buying boat stuff.