In the day-time scene in Ben's study, the words are darkened and the skull image has holes in the shape of teeth. Seconds later, is now in red and the skull is designed a little differently with the top of the mouth filled with teeth.
When it's first seen in the night scene from a distance, it looks like the "u" in Skull Cap has been replaced with an "i". There are also two other unidentifiable words after "Skull", although the last one is presumably "Cap". The "u" is missing when Fred Jones apologises to the Hex Girls. Also, when Mr. McKnight and Mayor Corey walk in, the words and image in Skull Cap's picture disappear (as with the other three pictures).