I assume the “epigenetic signature” they describe is some kind of methylation?

Indeedn. The linked article is terribly written.

Here's the paper instead: https://jamanetwork.com/journals/jamapsychiatry/article-abstract/2826082

It should be illegal to write an article on a study without linking the study.

Add it to the list

"It’s not clear what, if any, effect these epigenetic changes have in the lives of people"

No shit.

Also let's not pretend that the only response to scientific support of the existence of measurable negative epigenetic effects from generational trauma would be "being nicer." It could also be genetic discrimination. Or sterilization. Or eugenics. Or a tactic in genocidal campaigns.