Marko is a youtuber who creates lots of designs on everyday objects using paint pens and other artist mediums. He created this merchandise for his viewers to buy, which works as a form of self-promotion, when the viewers wear the shirt. The artist elements of his shirt and his cartoon character, based off of The Rugrats, shows what he really does and what his personality is like. I believe this is a good form of self-promotion because it gets his name out all around the world when his viewers choose to buy his shirt. It allows a large number of people to see it without a lot of effort on his end.

Website: https://dontsleep.shop