Thank you, very good feedback, I realy appreciate it. At the moment I'm not going to set up a mainstream brand, just a niche product for crypto and Bitcoin lovers. I dont think many people will like it! But I'm arguing... will the right people like it? Even if is a little niche I will be happy with it... Did you think is full?
I hugely doubt people will buy Bitcoin T-shirts and wear them in the streets.
LeGaulois said correctly, just t-shirt with bitcoin logo won't be popular but on another hand, T-shirts with I ❤ NY and Supreme T-shirts were very popular and behind them, there is great marketing that requires a lot of money and believe me, it doesn't worth for bitcoin t-shirts.
I think it worths for you to check these articles:
Why is Supreme so popular and this one -
Some information about I love NY.
Also, bitcoin shirt, crypto fashion and related keywords have very low search volume in google (in USA and UK definitely) while competition is pretty high because of Amazon, Aliexpress and others.
You won't find any commercial success here, I remember user Condoras was seriously taking this job, to make crypto themed puzzles but as far as I know, it failed
(check thread if interested).