"I Spotted A Few Of These Wrought Iron Poles On A Road In Central London, They Must Have Had Some Historical Usage, But I'm Not Sure What. Perhaps For Lamps? Did The Circle At The Top Used To Hold Something? Was The Arm On The Right For Hanging Something?"

Answer: "It's an early 19th C Gaslamp. The gas is piped up the pole, and a copper pipe would have extended into the glass lamp house, which fitted into the hoop."
Cabbage sliced for making sauerkraut.
5¼"disks came with stickers to cover up the notch to make them read/only again.
So the thing in not for write-protecting; quite the opposite actually.
Second this. Notch = writable, no notch (stick some tape or the like over it), write protected. If you wanted to use the back side of a single sided disk you had to punch three holes in the plastic housing, the write protect notch and two that would line up with the hole that marked the start of the track. We usually made a cardboard model of a disk to guide the punches as it required a fair degree of precision.
Single-side floppies were far cheaper than dual side, but at least by the time I was on the scene the chances of a failure on the back side were very low. I would guess we lost more due to not being careful enough when punching the sync holes than were bad from the factory. (One jaw of your punch had to go inside the housing and the disk was easy to scratch.)
I think you mean seat covers not toilet paper