I thought that there might already be something like that. I posted from something that was covered by WP/LAT but was not readily apparent (like a tv news station or smaller local paper) and quickly got a correction by the Admin Moderator. I know some and have viewed the list when I am unsure (like Atlanta Journal Constitution) but don't verify for every post.
Something that scans the source line would be good (although some aricles aren't apparent from that).
I know that I've had to hold off on posting some things from the Houston Chronicle (editorials mostly) that carry a Washington Post services credit near the byline. Some posters may not be as observant.