It's worth noting that none of the still-living BBs command a super high price for autographs as far as I can tell. All of them have remained (relatively speaking) accessible to either get an in-person autograph or purchase one through official means.
I wonder what the oddest BBs item that's autographed by a BB member would be. Like has Mike ever signed (or been asked to sign) a copy of POB? He did cowrite lyrics on a song there. Same with if Mike's ever been asked to sign Imagination, seeing as he wrote original lyrics for the BBs remakes.
I was sent a promo CD with "You're Welcome" on it circa 2002 (if memory serves) from the Carl Wilson Foundation after having attended one of their events; I assumed it was pretty rare, and I had Brian sign it at a GIOMH autograph signing, along with a DVD-Audio version of Pet Sounds.
I recall seeing clips of Dave being handed assorted BB albums he didn’t play on to sign during the C50 and thinking that’s not right. It was probably easier to sign them than not I guess.
Al has been signing copies of the Surfin USA LP for more than half a century, probably thousands of them, not to mention receiving gold record awards for it etc... David has a lot of catching up to do when it comes to signing stuff that's not right.