Each British gold medalist at the 2012 Olympics and Paralympics held in London got a post box painted gold in their neighbourhood. For additional gold medals, they get addtional post boxes!
Mo Farah lived and trained in Teddington, and a few years ago worked in a sports shop very near this box. That's why he chose this one apparently, but surely he has a sense of humour too?!
Fara is a charity formed in 1991 that supports needy children from Romania - they have 46 charity shops in the London area.