Actually, I think one of the clearest indications of a CREATIVE writer is the use of metaphors. In addition to that, I'd say flexibility and fluidity of thought are clear signs that someone is or would be a great CREATIVE writer.
I have a photographer friend who I KNOW would be a much better writer than I am because the metaphors come flowing out of her mouth and onto the keyboard effortlessly. Her facebook posts accompanying her photos are brilliant. She is able to compare one thing with something on one would have thought of.
Everyone who has language can "write". But when words come trippingly off the pen or tongue (like comics who do crowd work) that flexibility and fluidity of thought is a true indication "in my book" of writing ability. That being said, it's not to say (pardon that awkward phrase) that a writer can't imitate those abilities in his or her own writing. I'm the slowest person in the world to come up with a metaphor, but every ONCE and a while I do and then I'm pleased. I don't think we have to be gifted to be a good writer, just persistent and observant.