I have a 1969 Gibson ES-335 in a walnut finish that my father has owned ever since he special ordered it back in 1969. It looks just like any other 1969 ES-335 that I've seen except that it has an odd looking metal button in it. I took the guitar to a local Guitar Center store to do some minor investigation. They told me that they think the button is a stutter switch (kill switch). When they peaked inside the guitar, they told me that the switch seems to be as old as the guitar and made from genuine Gibson parts. However, they were highly skeptical that it came with this feature from the factory only because they haven't seen any other ES-335s like it before.
It's peculiar because there aren't any other 1969 ES-335s that came with this feature straight from the factory. However, my father is 100% certain that the guitar came with this stutter switch installed when he ordered it. My father isn't senile, so I believe him. So, this information leads me to believe that this guitar may be some sort of one-off production or perhaps a prototype that was accidentally sent out to my father.
I would definitely appreciate any information that anyone may have. Hopefully I can figure this out!