Why yes, that is George W. Bush's severed head on Game Of Thrones
You'd be forgiven for being far more concerned with an altogether-different severed head at the end of the first season of Game Of Thrones, but as revealed on the show's DVD commentary—and picked up by io9—it’s joined by another rotting skull of some minor political significance. While commenting on the spiked traitors lining King's Landing, executive producers David Benioff and D.B. Weiss reveal that "the last head on the left is George [W.] Bush," explaining that, while the rubber facsimile of Bush was used in several beheading scenes, they definitely didn't intend it as some sort of statement, even though it's kind of hard not to read it as such.
"We just had to use whatever head we had around," they say, as TV and movie sets are often plagued by mounds of discarded George W. Bush heads. Indeed, it's typically the job of some poor production assistant to clear them away each morning lest they prevent the talent from exiting their trailers, sometimes by piling them into the shape of distant mountains in the background, say, or in the case of New Year's Eve, Robert De Niro. Anyway, you can see Weiss and Benioff's slightly more novel method for disposing of them in the footage below, in which King Joffrey sneers at another unpopular, unprepared ruler thrust into power because of his name. (Note: We don't mean that in a political way.)