Just in case anyone actually fell for this little piece of viral marketing... you can't "sneak into" Platinum's offices. They're in a big, secure high-rise and you need to go through multiple layers of security (and a Michael Jackson exhibit) just to get to an elevator.
So what does this mean...?
Clearly this means that Platinum Games is the developer for the forthcoming Smash Bros. games, much like GameArts was for Brawl.
I know you're joking, but actually I used to go to the gym in the same building as the Platinum Games offices (Umeda Sky Building) and you needed absolutely nothing to get in there. Just sayin'

Same as where I work now. You could just get all the way to the main entrance of our office where the logo of our company is, and just sit there waiting until someone opened the door (which happens a lot).