In the 1960s some bright spark at Coca Cola came up with the idea of using the famous flocks of pigeons in St Mark's Square to advertise the company's name in a very eye-catching way.
It was not an original idea. Coca Cola had borrowed it from Assicurazioni Generali, a Venetian insurance company, which had its headquarters in the piazza. Assicurazioni Generali would regularly set out birdseed in such a way that the pigeons would form the letters A G.
A word of advice to any companies who might like to follow suit: since 2008 it has been against the law to feed the pigeons in Piazza San Marco.