The Phoenix Saga (3): Cry of the Banshee - S3-E5
Other mistake: When Xavier is telling Moira about how he and Lilandra were attacked, Moira dismisses his claim, reasoning that he came to her for help because he could no longer trust his own mind, and that no-one else had been in his room. She witnessed him flying out of a window, and he's a paraplegic. Unless she thinks he somehow catapulted himself out the window, she shouldn't have been so dismissive of his claim. Not to mention the damage to the room, including the bed being thrown against the TV. (00:05:21)
Chosen answer: It appears to be his initials "SH" in the style of the New York Yankees "NY" logo. He's also wearing pinstriped pajamas that look like the Yankees uniform.
Bishop73
I was expecting it to be some kind of Arabic symbol, but I can see the initials now, and it fits his character.
Phaneron ★