I think we had two OTA pay-TV systems back in the 80's.
I'm sure we had one called ON.
Not sure what the other was... but I seem to remember it was on channel 22.
They may have had positive sync (but that doesn't sound right...).
What I do remember is they inverted the picture (black for white) for a few seconds, then un-inverted it for a while.
An engineer friend described a large board of electronics and switches he built to decode it.
A three-bit or four-bit number was transmitted on line 22 (?) and then looked up by the decoder to determine whether to invert or not invert this particular frame.
Perhaps it was called: Select TV...?
Wow, it's been so many years!
But, it's enjoyable to dredge up these memories. -
We had something like that in Chicago called Telefirst which ran on our Local ABC station late night and I think had to be recorded played back with some box.
Oh......................... found a link . TELEFIRST