Not sure of the source, but the signature does look atypical to me. The signature is supposed to be representative of his signature style from around 1987-1990. I have never seen a legit SRV signature with a doodle like that or anything similar. I would run this past Epperson for QO, but my best guess is that this is likely a forgery unless you saw it signed.
Thanks - I did send it off to Roger for a quick opinion, I know he's also a major fan of SRV, I'll update with his thoughts. I was suspicious of the doodle, thinking it was placed as a distraction/diversion from the sig, but at the time I took the chance.
I heard back from Epperson on a quick opinion - he's "on the fence"... leaning towards not authentic... at least he did not come out and absolutely NG. Is it worth sending off to another authenticator?