This was mentioned on The Last Leg last night. Ian Stirling apparently used Gus Honeybun's birthday slot to give out coded messages to the gay community in Plymouth
I find this fascinating, and makes me wonder what other parts of TV presentation featured hidden LGBT messages during more restrictive times.
Maybe certain testcard/Ceefax tracks secretly revealed an LGBT continuity announcer or presenter of the forthcoming programme? Did the colour key for the mirror globe/clock ever “accidentally” go rainbow for a few seconds? Maybe the national anthem got replaced with ‘You Make Me Feel Mighty Real’ one night, blamed on a technical malfunction but actually a signal of a forthcoming Pride march?
As a slightly related aside, you might be interested to read up on Polari, the slang language used when homosexuality was still illegal in the U.K. It featured regularly in the BBC radio comedy series Round the Horne, although by that time it had become less commonplace in the gay community (according to Wikipedia).
Coded messages for the resistance were used during the Second World War in broadcasts to France hidden in some of the messages from home.
Are there any other known ones?