Sounds like a lot of work to get such a project off the ground. You'd need an extensive database of potential advertisers – local businesses for locales scattered across the planet.

To compile such a database and make sales pitches to everybody within it, you'd need a sales staff fluent in multiple languages, familiar with the layout of cities all over the world.

And to convince them to sign up, you'd need an army of travelers ready to wear the T-shirts – which, by the way, you'd need to manufacture and ship. Those T-shirts would showcase a long list of local businesses; yet volume for each shirt would probably be low.

To manage all those challenges, you'd probably have to give up traveling and work out of a cubicle, where you'd be able to focus on writing emails and making phone calls. Would you? I'm guessing not.