Probably signed it when he sold it. IIRC he was the guy that convinced Yamaha to build the J1 and J2 lines based on mods to a SBV-550 he made for Lâarc-en-Ciel, and he had a few of each. He may have signed them all but I doubt it, probably just his.
He also produced Polysics, which is probably how Fumi got in to them.
edit: actually I just looked it up and Fumi is the one that turned him on to the SBV
terrible translation of what I read:
âWhen producing Polysics, he also liked YAMAHAâs SBV bass used by their bassist Fumi, and produced a limited edition of 100 SBV-J1/J2 in collaboration with YAMAHA. Although it is inexpensive, the SBV is evaluated as an excellent bass that can be used in professional situations.â
That last sentence pretty much sums up most Yamaha basses