Am I the only one using old paper??
I've been using vintage B&W paper for lumen prints, and have several different kinds of Kodak paper I haven't used yet. Some of the prints I did on Velox have 'A KODAK PAPER' w/the trademark R on the back - all caps but KODAK is in larger letters than the rest. That batch was from paper that expired in 12/66 (saved the label). It's 2 1/2 x 3 1/2 inches but I have similar paper (Velox, Kodabromide) in various sizes that were manufactured within a few years of each other.
Even though I have mostly paper for B&W prints it looks like the same watermark may have been used for that as well as color. The closest to that I have is Panalure, which is for B&W prints from color negatives.
I don't seem to have any so far from the era you're looking at (later '60's thru the 70s?), but I haven't looked thru my whole stash yet. I have old paper going back to some that expired in 1909 (so I'm about 100 years too late to take them up on their offer to replace the paper!) and some Azo that says it can be developed by gaslight.
What else do you have to go on? - gogo boots? bell bottoms?? maybe we can help narrow it down that way!