Keybase would have been a good solution, essentially a GUI for a pgp keyserver but with social proofs like "the owner of this account also controls the domain washingtonpost.com (as evidenced by publishing the fingerprint as a TXT record)". Too bad about the zoom acquisition, development stalled since then.

I also don't know exactly what bag of bytes you would be checking the signature against, the raw normalized text of an story? Maybe if news articles were distributed as PDFs this would be a solved problem, but news sites actually don't want their content to be portable, they want you to sign in to their domain to view anything.