It doesn't matter here, since the asker presumably wants US English, but it would be nice to know for future reference.
I don't think it has a traditional name, probably because it isn't a traditional feature of British newspapers. Here's Bill Hagerty referring to it in the Independent; if there were a familiar term, I think he'd have used it:
"Then he advocates the prominent publication, in every copy of our papers, of the name of the editor and of the readers' editor, together with contact information.
The second of Soley's suggestions seems straightforward enough. Many regional papers and most of those published in the United States already supply such information, often below a reproduction of the masthead on the editorial page."
http://www.independent.co.uk/news/media/bill-hagerty-on-the-...You might call it an editorial credits box, or something like that. But although "masthead" in the UK means something else, I think it is also acquiring the additional meaning it has in the US, the basis of which is probably the habit of printing the editorial credits on the editorial page under the masthead, as Hagerty indicates.