Unfortunately from personal experience, this is becoming rarer, and I would no longer equate open source with open trademarks. The most egregious I’ve seen is

Unfortunately from personal experience, this is becoming rarer, and I would no longer equate open source with open trademarks. The most egregious I’ve seen is an “open source” hardware company also trademark a term within an education trademark class that technically prevented others from advertising their own seminars or workshops.