it is just you (kidding). How would they hear of you? Why not wear a t-shirt! T-shirts are a pretty low-cost investment in promotion. I can buy a black shirt with a single color imprint for $3.50 in small runs. A good pen with the company name on it would cost the same. (source: I have been buying giveaway crud for 20+ years)
Giving away a metric ton of shirts can have some other interesting effects. In the early days of my manufacturing company we gave away many shirts to people within the industry. We started getting calls about 'our people' attending events that we did not attend. It turns out that some of our customers really saw other customers at trade events, but there were so many people with our company shirt on that they impression was that we were attending in force - we werent at the trade event.
After giving away 20,000 shirts in a four year period, our customers started complaining about having too many shirts. So the technique does not last forever. It did always amaze me the delight a grown adult would show when they were given a $3 shirt. Almost always a better investment than a pen.
Best ideas: Have a decent looking shirt that people want to wear; change base shirt colors so people can have an option. Some people like blue, some like red. Give them what they want, it doesn't change the cost of the shirt.