The only way to know is to see it in person and look to see if it's really sharpie ink sitting on top of the litho, and if it's really written by hand as opposed to an auto-pen (which is slower, so a lot more ink soaks into the paper, and there are no streaks like you'd get with a faster pen stroke).
$400 may be high for this depending on the size of the frame and whether it's one of a limited edition or a unique item. It's not a vintage item, and it's not from a more legendary album, but it's definitely worth something if the signatures are real. I'd make an offer if I didn't already have a 2112 litho, hand-signed and framed, w/paperwork, etc. (long story, but let's just say I lucked out and got a ridiculous deal on it).