To the best of my recollection, it's until very recently been used primarily or only for questions that present a statement, halacha, or idea and seek only a source for it.
In the past few days, however, I've seen it used also for questions that seek both a definitive statement or halacha and a source for it. (I've undone a few such taggings, in line with the older usage.)
What should we do with this tag? Some possibilities are:
Use it as in #1 above.
Use it as in #2 above.
Don't use it.
Please propose these or other ideas as answers so people may vote them up or down. (Votes on this question will be meaningless.)
I propose we get rid of the tag. Tags are good for search engines (a question tagged passover will be findable when one searches for Passover even if the word Passover isn't in the question), for browsing (people can browse all Passover-related questions at the tag page and can 'favorite' or 'ignore' specific tags), and for identification (people can see what a question's about by glancing at its tags). None of these seems applicable to the sources-mekorot tag.