Slam was looking for another MD
-80 manual. The one nearest to hand did not depict the yellow spot.
Best I can recall DC-9/MD-80 had the oxygen blowout disk (green) on the lower right fuselage, just forward of the bag pit and very near the bottle.
A yellow blowout disk would be for overpressure discharge of the fire bottles but that should be somewhere within one airplanelength of the fire extinguishing system - in other words, near the engines and APU.
It also looks too big to be one of these plastic disks as I remember them being no bigger than a nickel. That object seems to be at least two fingers wide, measuring by the captain's hand.
Rain repellant blowout disk?
Waiting for an AA
MadDog pilot or mechanic to jump in.
Happiness is not seeing another trite Ste. Maarten photo all week long.