Sure, I just (honestly) wondered about trademarks.

https://apertus.org/about

>> "The "o" stands for "open", "openness", "open source" and is placed where a "TM" symbol (indicating patents, trademarks, protection) would normally reside. Instead openness is the apertus° trademark."

It's also a completely different kind of thing so trademark probably wouldn't come into it even if they had one.