What citation / reference styles explicitly tell the reference's type?
Well, as you see, such style exists, at least in your question. Remember that while references have to satisfy some minimal criteria, there is not much more rules and the styles vary a lot. So certainly, if you take any widely used style and you add (book), (journal article), (webpage) or whatever at the end of each citation, you create a new bibliography style that complies with the rules. If you really need to distinguish it like this, then what you shown looks usable, just please for Gutenberg's sake, don't make it all-caps.