I hadn’t spotted that these were just on BBC channels and I believe you are right about the solid circle, Barry.
On the programmes showing this when I pressed OK there was an option to ‘Watch Now’ which took me to iPlayer.
However I’m not sure about your idea regarding the broken circle, as it is showing on some programmes not yet being broadcast, at 00:15 it was on a BBCFour programme due to start at 1:05am, and I can only see the usual options when I press OK i.e. no ‘Watch Now’ option.
It is also showing on some past programmes with no option other than ‘Close’ after pressing OK.