A recurring visual feature of the [Hong Kong] protests has been the so-called Lennon Walls, where people have posted hundreds or even thousands of slogans — mostly on Post-it notes — in public spaces across the city.
Their name comes from a wall in Prague where tributes to John Lennon appeared after the former Beatle’s killing in 1980. It evolved into a place where young Czechs expressed support for democracy and aired grievances against the Communist regime ruling Czechoslovakia. ["Fueling the Hong Kong Protests: A World of Pop-Culture Memes," New York Times, Aug. 2, 2019] 
Definitions of Lennon

Lennon (n.)
English rock star and guitarist and songwriter who with Paul McCartney wrote most of the music for the Beatles (1940-1980);
Synonyms: John Lennon