As you well know, I'm opposed to violent rhetoric on principle and should be offended, but honestly? A second-long Easter egg that no one notices until the producers point it out in the DVD commentary doesn't really qualify as a pointed rhetorical statement. Not that it won't be spun into one as soon as someone emails that link to Jonah Goldberg or Jeff Goldstein—both of whom will point out that it'd be considered both violent and racist if it were Obama's head—but it's still an Easter egg, which by definition limits its appeal to the Bush-hating, Martin-loving, DVD-commentary-watching crowd, which likely numbers in the tens.
That said, I don't buy the producers' claim that it wasn't "a choice [or] a political statement. We just had to use whatever head we had around." The scenes in King's Landing were filmed in Malta, so I find it difficult to believe they happened to have a plastic replica of W.'s head just lying around. Unless there's a booming Maltese trade in eerily life-like effigies of which I'm unaware, that Easter egg was planted there purposely.
Rhetoric aside, there's all sorts of fun to be had with this, including (but not limited to) questions such as "What's the sigil of House Bush?" I contend it'd be this:
A root-rotten shrub surrounded by all the weapons of mass destruction W. found in Iraq. Feel free to offer your own suggestions in the comments.