Maybelline, Burger King, Nike, KFC and McDonald’s seem to have the most catchy straplines that people recognize best. 

Back in July, the biggest U.K. media company CBS Outdoor in collaboration with creative agency Clinic launched a two-week campaign to celebrate 150 years of advertising on the London Underground. The commuters were offered an online free game featuring a puzzle of product shots or straplines of 150 popular consumer brands. Due to the tricky nature of the quiz, just 700 players managed to guess all the brand names correctly, while one of them won a one-year free travel in the tube; for 100 correct answers Londonders could get a six-month paid travel, for 50—one free month.

The campaign was massively advertised through 115 posters across 78 stations on the Tube, as well as through a hashtag #150brands in social media. The total reach of the game was incredible—not only London commuters but an international audience of 22,419 unique users from 99 countries played the game for an average of 47 minutes on their smartphones and desktops, making over 1.5 million guesses. About 31% of the Londoners played the game on their mobile devices using free WiFi, Simon Harrington, marketing director of CBS Outdoor, admits. About 39% of them came from social networks, 37%—from referring websites, and 50% came on the game site directly after seeing the posters on the Underground.

This campaign for TfL, marking 150th anniversary of the London Underground came as a follow-up to CBS Outdoor’s «Look for Longer» game, launched last year.