I don't think it's marked in my tires, but it certainly is printed in the manual: 29 PSI front, 30 PSI rear for stock sized tires. Manual asks to add about 2 pounds more if a lot of high speed (100 mph) cruising or if you're carrying heavy load/passenger.
When I was a newbie, I didn't realize my rear tire was at 20 psi or below and it was seriously messing up the handling, the rear would wobble on curves.
Proud owner of stock '76 CB750.