It’s just vinyl lettering made for boats. It is installed just using soapy water and a stiff squeegee kind of scraper. Super easy. They can be ordered at CLC or many marine supply places. No sealant required. Easiest part of the entire project!
CLC link and installation video. http://www.clcboats.com/shop/boat-building-supplies-epoxy-fiberglass-plywood/vinyl-boat-lettering/