Susie Sahim, the artist behind many of Google's event-based logos and and known to appreciate Legend of Zelda—and Link in particular, is believed to be have deliberately hidden tiny TriForces in her work. Neither she nor Google would confirm or deny anything.
I have to say that I looked at these logos a bunch of times during random, daily Internet searches for game-related material, but I missed the appearance of the TriForce each and every time. Given their small size, it's no wonder they remained hidden for almost two years.
That's pretty gutsy though—hiding the copyrighted property of one giant, heartless, litigious corporation into the logo of an even bigger, heartless, litigious corporation.
Source: Google Blogoscoped