Hi Mark
I think I understand what you're getting at, but I don't think you're correct.
If something is PD, then it's not under copyright or trademark. So you can do what you like with it. That's what PD means.
I guess the distinction is, since "characters" aren't specifically protected by copyright (they are a part of work they appeared in), the name or image might be trademarked if its still in use.
When the Golden Age Daredevil trademark lapsed, Marvel was able to use it - now you can't advertise your comic about the GA Daredevil using the name 'Daredevil'.
I'm not sure how the imagery (i.e. how the GAD looks) is something Marvel (or anyone) could have used and re-established a TM on it. Various companies have used the GAD in their comics and don't seem to have TM on it.
And it makes no sense to say that if a character is PD you can't change it if it's trademarked. If its trademarked, its not PD; if its PD, its not trademarked. I think. Again - can you trademark the image of the character? Not sure.
Ah!!! Roy what I was trying to show was just because a work is in the Public Domain you can't 100% safely take it and use it for whatever you want.
You CAN if none of the characters are trademarked but you CAN'T if they are. See what I was getting at?
If it is truly public domain and you leave AS IS then you have no worries. but if you start alerting it then you have to make sure that none of the characters are trademarked
So in very simple terms get hold of a standard horror, romance or crime that is PD you should be safe to mess around with it. But a superhero story might lead you into trouble. I was also trying to say that if you were starting to make a buck just be aware that you might find strange claims being made. Trademarks seem a real kettle of fish and a great way for lawyers to top up their pension funds .... lol