Conserving autographs

xphobe

I've got a photo of Harry Truman and me. My folks put it in a frame with a beveled mat and he signed the mat.

Problem is, the writing is fading out, probably due to years of light on the wall. Is there a way to "fix" ink or bring back the dark color? Can anyone recommend a professional for this kind of thing?

Also, any idea what it might be worth on the market? Not that I want to sell it, just curious...

Thanks!