[edit] A few people have tweeted surprise about interpreting the slogan this way, and the organisers have commented to note that the double-meaning wasn't intentional.
We've had some great Drupalcon t-shirts over the years. London played on its punk heritage with a Druplicon roundel design inspired by The Who, Munich referenced classic Bavarian dress, Denver incorporated the region's climbing axe symbology…
At Drupalcon Prague, the official T-shirt punned database terminology against Prague's stag city reputation, with the slogan 'One to many'.