@welshpixie Trademarks are not only geographically limited, but also limited to a business field. Hypothetically you could start a Starbucks record company and be in the clear, but in practice huge corps have superior bullying power. But for corp vs corp, see e.g. Apple Records vs Apple Computers.

But yeah, a business that has no presence in a country generally can't say anything about their trademark. And, as you noted, there's no Mamma Mia pizza chain, so every town has a local Mamma Mia (and another dozen pizzeria trope names) and it's totally fine.