The practice of placing cards was known as carding. It is a particularly English phenomenon specific to London and seaside resort around Brighton and Hove (though they did appear in other towns) For the printers who were prepared to take the risk they represented a very regular and lucrative business.
Sex sells but ironically sex was the one word that was not used on the cards. Hand written, euphemism, double entendres, catch phrases, plain text, rhymes and a specialised vocabulary.
There was a lot of competition so their business cards had to stand out from all the others.
Have a fun weekend.