The only time I remember seeing pre-signed merch, was on Gigantour, and there is a kicker to that. Every other band (including Megadeth, if memory recalls), would sell their latest album at the show, among other merch. If you bought that recent and overpriced album, there would be a time to go by the merch stand and have the band sign it, personally. Dream Theater was the only exception, pre-signing Octavarium and just making it available to buy.