You'll need to learn more about, and better define your two personas:
A) The type of company willing to pay for t-shirt based advertising
B) The type of person that will to wear it.

To do this you'll need to access communities where you think those personas would hang out (either online, or in person), and ask them questions (via an online questionnaire, or in an in person interview) that will allow you to characterize the types of people / companies that would be interested.

Once you have your two well defined personas you can better design and test your initial service around them.

For instance, maybe you've realized through your research that only bars are interested in your service, and maybe they're only interested in women wearing their advertisements. Meanwhile you might have also found that only men would be interested in wearing the advertisement shirts. In this case the idea would not be viable.

However if you find personas that do match, and there are enough of them in existance (big enough market), and/or they're interested in paying enough $ (enough to pay for the t-shirts, and your rent, and cleaning, and occasional lost shirts, etc.), then it would be viable. Not _necessarily_ the next big thing, but definitely viable.

Let me know if you'd like more detailed advice with regard to conducting interviews, designing questionnaires, how to access potential customers, or even if you'd just like to brainstorm on it some more. It's a fun idea,

best,

Lee

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.

If you ask me if the question is viable or not, it will be a bit difficult to judge given whatever rough sketch of your idea you have given. To understand if a question is truly viable or not you must keep the following points in mind:
1) You have a clear business plan for it
If the way to hell is paved with good intentions, the road to failure must be paved with half-baked efforts. 20% of new businesses fail in their first year, 30% fail in their second year, and 50% fail in year 5. These are pretty daunting statistics. The most common reasons for new businesses failing are poor management, lack of planning, insufficient capital, and cash flow problems. However, you do have full control over how you run your business. There is plenty of advice floating around on how to manage a business properly, but most of it can be boiled down into one simple truth: you must have a clear idea of your past, present, and future. To avoid losing sight of the wood for the trees, it is helpful to have a high-level statement to refer to periodically. Knowing your present means you’re confident that you have the skills you need in your organisation, your expenses are kept lower than your income, your processes are smooth, and you’re getting honest feedback from your customers.
2) You have the means to move forward with it
You may be inspired by stories of entrepreneurs who sunk their last penny into their business idea and are now millionaires. However, for every success story, there are untold failures. For example, if you approach a bank for most of the capital needed to start up, you are at the institution’s mercy for years. You will be responsible for the repayment, often on draconian terms, whether your business works out or not. Perhaps you have just started a family. Instead of diving headfirst into a venture, it pays to plan. You may want to amass some savings first, to bring down your loan requirements. You may want to make changes to your lifestyle.
3) Someone in the industry thinks it is a good idea
If you are familiar with the industry already, that is a bonus. Your own expertise and knowledge has told you that you’re onto something. However, you should always get a second opinion. Just as a writer needs an editor to cast an objective eye over the material without the bias of being its creator, you will need someone to point out the things you have overlooked. They will be able to tell you exactly what the gaps in the industry are, what problems it faces, and what obstacles stand in the way of change. If you are trying to solve a problem, it is likely someone else has already tried to do so. And there might be particularly good reasons why they have not been able to do it. If someone who knows the industry well thinks your idea will not work – that is a profoundly serious warning sign. That is why at the idea generation stage, you should not restrict yourself. This is when you should be pulling things out of left field and coming up with the most creative and innovative things you are capable of. Getting the opinion of an outside party comes in the elimination stage when you are deciding which ideas to go forward with. A second opinion is to help you judge your ideas more objectively and make you aware of vulnerabilities in it.
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath