See what you mean: the Yamaha Revstar doesn’t have Yamaha on the headstock, but does have the tuning forks.

But other Yamahas don’t have the tuning forks but do say Yamaha. Eg. https://uk.yamaha.com/en/products/musical_instruments/guitars_basses/el_guitars/sg/index.html

I think there was a period, pre Revstar, when motorbikes had the tuning forks but none of the Yamaha guitars did.

Yamaha makes lots of other musical instruments too.

The thing that puzzles me is that the Yamaha logo, 3 tuning forks, makes sense for instruments that you tune. But I’ve only seen it on their motorbikes.