Tart cards are cards advertising the services of prostitutes. They are found in many countries, usually in capital cities or red-light districts. Originating in the 1960s, the cards are placed in locations such as newsagents' windows or telephone boxes. Alternatively they are handed out or dropped in the street.

The cards originated in the 1960s in places such as Soho, London, as handwritten postcards outside prostitutes' flats or in the windows of newsagents or shops. As direct references to prostitution would generally be unacceptable, the cards were carefully worded and often contained euphemistic references to sex, with terms such as large chest for sale.

By the late 1980s tart cards had become black-and-white photocopied cards containing printed text and telephone numbers. The cards from the 1980s and 1990s often included black-and-white drawings printed on neon-coloured card along with tongue-in-cheek phrases. In larger cities, the cards were placed in phone boxes.

Quoted from Wikipedia.