Real easy to "add" stickers during a photo op. Ever seen a NASCAR driver changing sponsor hats during an interview?
I would submit that those stickers were likely added during the photo session in anticipation of the STP sponsorship deal.
Regardless interesting bit of photo trivia.
If you look at the shadows under the bike in the three pictures, it looks to me that Freuds picture was shot first and the other two pictures a bit later in the day, as the shadows are farther back on the second of the pictures with decals than the first. That implies the bike was on display for some period of time, making minor setup changes like adding the stickers a 30 second change for a new picture setup.
Larry