I've used something similar but not sure who we got it from (was many years ago).

I think we had to provide our VIN and they sent back the kit with several cardboard strips with the VIN cut out (about the thickness of a manilla folder) and a small vial of "stuff" - basically you place the cardboard on the window, "paint" over the VIN number cutouts with the gunk, wait a while and rinse it off. It seemed to work fairly well - I think on one window we either didn't use enough or washed it off a little early as it didn't seem as defined as the others but overall we were satisfied.