I think wearing clothing with a logo raises awareness of the marque.
I was moving my son into college last year, and another dad remarked how much he liked my 'Norton' shirt (BRG with gold logo). He then asked if I worked for Norton, and if I knew when their next anti-virus was coming out.
I replied that Norton was actually a British motorcycle make, like Vincent (blank stare), Matchless (blank stare), BSA (blank stare) and Triumph (eyes light up).
I have Ducati, Guzzi, and BSA shirts, but currently don't have any - and I wear them anyway.