Since those are charcoal and/or pencil, (if they were mine), I would, for sure, get them framed, and placed under UV plexi. The thing to do with these, and because each one looks to have a rather wide, blank border around the artwork, would be to have your framer cut a mat with the opening slightly larger than the images/signature- maybe a 1/4" or so, all the way around.
That way, the mat isnt pressing or directly touching the artwork, won't smudge it, and will also act as a layer that keeps the plexi directly off of the art. Plus you will see the signatures, too.
Again, that series of drawings is just very cool!