Maybe it was enough that the policeman didn't pull his hand away, and looked over at the other chap? Perhaps that was all the communication that was needed?
Ppeatfruit - I love the Lord Peter Wimsey novels, and in one of them he works at an advertising agency, who advertise cigarettes, amongst other things, and there is discussion about different adverts, from different agencies, for the different brands, talking about how one will say it is good for the lungs, and another will then get a leading physician to say their brand boosts lung power, and so on. In a side plot to the detecting bit, Lord Peter thinks up an advertising campaign for Whifflets cigarettes, where each pack contains a token, and you can collect for all sorts of things - day trips, holidays, weddings, houses, cradles, even a kit airplane - the tagline being 'Whiffle your way round Britain'. I loved that plot.