The letters are individual stickers on an adhesive strip, so wet the surface with glass cleaner (don't dry off the cleaner), press the letters (with outer strip still on) onto the surface (use a level to make sure it's level) and then peel off the outer strip. It's like putting decals/stickers on an automobile.
Die Cut Glass Window Decal : Fire Extinguisher Part #:LB-1949 15" x 1.5" Die-Cut Vinyl with Back Adhesive Verified PurchaseFire Extinguisher labels - pretty good
Takes a little bit of skill to apply since they're individual letters.