@motcha11
While your shul may say no one should tell someone else that he is seated in someone else’s seat, I don’t believe that should apply to seats in shuls that are sold for major donations and have name plaques on them.
A visitor should not presume to seat at a seat with a nameplate unless directed there by the gabbai.
When I was growing up in New Haven, it was common for families to belong to multiple shuls and pay dues to each and have permanently purchased seats. I remember on Yom Kippur my father would start the day with us boys at one shul and make the rounds of 3 or 4 shuls during the day, greeting friends and relatives. In each shul, the family seats would be open awaiting our arrival. He varied the order each year.
When my father was niftar in 1989, I received 3 nameplates in the mail from shuls where he had purchased a permanent seat.