This morning I was squeezed on to the Bakerloo line re-reading The Tipping Point. A central premise to creating tipping points is the power of word of mouth. I'm in the middle of this bit as we approach Oxford Circus. Over the tannoy a remarkably cheery female Irish voice informs us of our next destination. She then went on to say "Now, I'm going to let you in on a little secret. There's a shop up there somewhere called Selfridges. And if you get there quickly they're handing out free chocolate for Valentine's. I gather it's being handed out by scantily clad young ladies so there's something there for the fellas. Anyway, it's just our secret, don't tell anyone, 'cos I'm there myself straight after work".

There are two possibilities here. 1, Selfridges has incentivised Underground workers to promote the store. 2, She'd heard about the promotion somewhere and was enjoying her ability to broadcast it on.

The 'professional' side of me hopes that it's a great piece of media freethinking, a commercial message planted by a commercial organisation in an inventive and positively disruptive way. However, personally I hope that this charismatic tube guard was merely trying to brighten our day, and in so doing enhancing footfall at Selfridges by using the most powerful medium known to man - the transmission of an idea by word of mouth.