Among the professional journalists I've known (quite a few since I went to journalism school and worked in a newsroom for four years), licensing has been universally seen as a Bad Idea. The reason being that this gives the licensing authority power to decide who deserves to be recognized as a credible journalist, which is one very small step away from power over deciding right/wrong-think, which is antithetical to the point of journalism.

Perhaps a compromise is to identify a journalist by the news network they're associated with.