The vendor calls them Decals....But we can still persecute the poster.

The English language allows for Vinyl decal or vinyl sticker or Sticker, decal or label. All used interchangeably in the industry. Many companies call them vinyl decals, Classic Parts of America calls the oil filter label: "waterless decal".
Bottom line: He wants to know if/how to seal them. I agree they do not need any coating and should not be coated. The instructions do not say to do that.