I listed a photographic negative for sale on eBay. The subject was a train and the shot was taken at a public event (fair) in 1949. The photographer was a private citizen unconnected to the train or fair. I was notified - threatened actually - with legal action if I did not place an acknowledgement of a person and a foundation in my auction page. I pulled the auction and before I relist do I need to comply, ignore it, or add tm after the phrase?This person claims to co-own the name of the train.