It seems some posters here think Mr Wilson's assistance may sign fir him and include the Parkinson's related squiggles.
Just let that sit for a moment: Parkinson's related instability included.
Yeah, sounds beyond the scope of reality and all that is good in the world, doesn't it?
As one of you mentioned, like Beach Boys or not, Brian was a genius up there with Les Paul, Martin and The Beatles, etc. Pet sounds should be given a listen to by every musician at least once.
Find out the charity and then contact mr Wilson's handlers for verification. If it's good, and provable, sell it to someone that values it for $300 and get one that doesn't have a sig.
...and like many geniuses, he was always a little "off" in some categories (being good buds with Charles Manson, for example)... My vote - if it's not provable / documented, probably little or no monetary value now, wipe it off... ...then again, running by eBay to see if anyone values it for the sig seems reasonable too.