The phrase comes from Dutch fairground culture, where operators at a kermis traditionally call out to visitors to buy tickets before using an attraction. Koop uw kaartjes is the polite formal form, using uw rather than a casual your, which gives the clip its slightly old fashioned official sound. As a short isolated voice clip it has circulated on soundboards as a reusable announcement, detached from any single ride or fair. Dutch speakers recognise it instantly, while other viewers use it purely for its urgent carnival barker energy.