Sticky-backed and just smaller than a postcard, I'd guess that this was the launch sticker for Greater London Radio (GLR).  Other versions of this logo have the BBC logo just above the 94.

BBC Radio London launched in 1970 and lasting with this name until 1988.  It became Greater London Radio (GLR) for the next 12 years.  2000 saw it relaunched as BBC London Live.  A year later and another name change, this time BBC LDN and then BBC London 94.9.  Am I the only one who thinks BBC Radio London is the best name for it?