In the time before factory and aftermarket a/c could be better-afforded, plus many people ordering tinted glass, there were some roll-up screens for the side windows and Venitian Blinds for the rear window. Never did see one like the one in the picture, but it's obviously a more expensive item than the roll-up screens.
Back then, too, my parents would comment about "Bet that rear seat gets hot in the summer", due to the shape and angle of the back glass, where the rear seat was in relation to the back glass, and the roof line. Maybe one of the reasons the "flat top" GM 4-dr hardtops were popular in the earlier 1960s?
One of our Mopar cluib members had an Anniversary Gold '64 Polara 2-dr hardtop. Had the "custom fit" Venitian Blinds in the back. Looked pretty good!
Enjoy!
CBODY67