Do You Find Advertising On USPS Trucks Effective?

I was just walking down 2nd Avenue in Manhattan with a street flooded with outdoor advertising, commercial messaging, branded buses and decorated vehicles abound when a USPS truck trundled by with a Superman 2 ad
I could see on its side … and then I turned and looked again. I suddenly realized there was something oddly unique about it being a USPS truck that for me made the use of advertising even more effective.

You can hardly call USPS a halo affect, but brands are personalities and USPS is uniquely one you want to trust. Least I think so. Maybe that’s the trigger for the second look I gave it? I’m not a Superman customer so it had to be something that drew me back to look again and think again. I’ve trawled the web in search of any stats on its effectiveness and can find none, but using USPS trucks (USPS have over 220,000 vehicles) as the medium impacted my ‘double turn’ attention that soaked in the medium and the message – it was just the wrong ad.