Ambiguous signs/notices (London)

Lots of pillar boxes in London used to have two compartments, marked “London” and “Country”.  I was once standing by one of these when I overheard a baffled American tourist ask, “Which country?”

This sign along the side of London Tube escalators is increasingly disappearing now:  “Dogs must be carried.”  Someone once asked, “What if I don't have a dog?”  Someone else asked, “Where do I get one?”  

(London)

*pillar box: (in the UK) a large red cylindrical public postbox.