Interesting poster. Saw it yesterday in the London Angel tube station. I wonder if it is a random one-off or part of a series of a "make people-wonder-what-it-means-and-then-surprise-them"-multi-poster-campaign.
Maybe someone just wanted to give a kiss to the people. Which actually reminds me that the habbit of putting an x as a kiss in the end of emails, letters or text messages is a thing that is very common in the UK - but completely non existing in Germany where I'm from. So I wonder if it is just a British thing or if other countries have adopted it as well? And where did it come from? And since when means "xxx" I love you?