Info requested: Double Seamaster caseback logo

Hi all, new to the forums and hopeful you can help. I'm considering a vintage Omega Seamaster 600, by all account is pretty normal, save for one detail. On the caseback, in addition to the Seamaster logo, there's a second logo that I'm unfamiliar with. By the way the original Seamaster logo is shifted, I'm inclined to think that it's original to the watch, so wondering if anyone has come across this logo before? If so, what is it in reference to? Or, could it have been added later on? The watch in question is a ref: 135.011 with a 601 manual-wind movement. Any help is appreciated. Thank you!!

Thank you so much. I was scouring the internet trying to find something relevant. Much appreciated!!