Archiving pictures I took with my phone, found this calligraphic beauty from Copenhagenpic.twitter.com/9ogHR4W2hS
You can add location information to your Tweets, such as your city or precise location, from the web and via third-party applications. You always have the option to delete your Tweet location history. Learn more
Who even sells those?
Not sure but they're common grafitti (tag) apparel. These might be a bit larger than your example, though. :)
Twitter may be over capacity or experiencing a momentary hiccup. Try again or visit Twitter Status for more information.