Hey guys -- I apologize for the poster -- that was MY bad. There's lots of these little things that makes our ecommerce software problematic and hard to maintain for some things. This is one of them.
If you did add a signed poster to your shopping cart, you were getting sale prices, they just didn't jive with the display of sale prices on the index pages with the little thumbnails.
That's all fixed now, the unsigned posters are now out of stock, and the signed posters remain, at 80% discount through noon tomorrow, so grab'em while ya can.