So Super Mario Bros. released on the NES in 1985. We ran out of fingers and toes trying to figure out how long ago that was, but our theory is 25 years.
We feel pretty good about this theory in light of a recent trademark filing by Nintendo of this here image. It doesn't say "25" anywhere on it, but you don't exactly see companies filing trademarks for their head mascot's 23rd anniversary.
Nintendo has yet to reveal what it plans to stick the logo on, but Kotaku notes that the company used a similar logo for Mario's 20th anniversary and one that appeared on a special Famicom-themed Game Boy Micro. It's possible Nintendo has similar plans for a special DS, or it might just be for that special Super Mario All-Stars reissue.
Either way, whatever it gets stamped on will likely appeal to retro enthusiasts and those whose inner child controls the wallet.