Ah, a staple of 1980s late night channel 4 pink triangle (which sounds worse than it was) telly. Those were the days...
https://www.bbc.co.uk/news/entertainment-arts-46709681
For you non-brits and young uns too familiar with easily available naked people on your ipads, when the great and the good complained about too much smut on the brand new TV channel, they responded by putting a pink triangle in the corner of the screen when bare bosoms, arses and occasionally much more was about to appear. Obviously it meant you could generally ignore some tediously slow foreign arty bollocks and keep half an eye out for the triangle to appear. Happy days, lol oo haven't overshared for a while.