Yes, that is an exclamation point (!) on the back of her neck and head, inked by Mony at Body Graphics Tattoo in Philadelphia.
So why an exclamation point? Sam explained that, in the video game Metal Gear Solid on the Nintendo System, an exclamation point appeared over a character's head when he was spotted by a villain. The programming was very basic, so when the technology developed to improve on the (!) appearing over the head, the makers of the game kept the symbol, and it became
somewhat camp.
Sam remarked that her nod to "low culture" is offset by this tattoo which is on her outer right arm:
I recognized the insignia immediately, having read Thomas Pynchon's The Crying of Lot 49 in college. Sam reminded me that this symbol is that of the muted post-horn, a key plot element in the novel.
This is her "high culture" tattoo to complement her video game punctuation mark.
Thanks again to Sam for sharing her interesting tattoos with us here on Tattoosday!