As Lowering the Bar points out, if there’s a goofy trademark claim − in this case trademarking the mathematical symbol “pi” but why would someone want to do this anyway and why would any patent and trademark office put a good housekeeping stamp on such a thing? − there will be a goofy “cease and desist” letter from a lawyer.
Since I wasn’t able to identify the Greek symbol for “pi” in my symbol collection, I withdraw myself for any debate, because I don’t understand it.
I fear I will spend a few minutes today wondering what nutty thing I could trademark and then a few more minutes asking myself why.
P.S. It must because I have a cold and my head is fuzzy that I didn’t see the very large Π symbol on that t-shirt. So there it is, there is “pi.” And the Zazzle t-shirt company is resolutely producing their Π t-shirts. Bravo.