Should we really expect anything? Does USA, ESPN or any other channel acknowledge every anniversary? (Heck, I don't even know when USA's anniversary is!) I'd expect that GSN will probably acknowledge important ones - like 15, 20, etc. They at least acknowledged their 10th with that GSN moments montage that was mentioned. I believe it also aired full screen as a commercial during shows as well.
What I'd eventually like to see is an anniversary montage like they did their first couple of years, by airing one episode from every series in their holdings. Some of those shows haven't been seen in a l-o-n-g time!