FWIW - I sign on the back in pencil and include the print date. I also sign the matt on the front. I offer my prints matted (in most cases) for protection and presentation purposes. Buyers also receive a "certificate" card as shown.
Below the printed image in the white paper margin, I use Lightroom's Identity Plate in the Page palette of the Print Module to print "An original photograph by Terry A. McDonald – www.luxBorealis.com
" as well as the "Photo Info" (also in the Page palette) to print the "Title" from my metadata. If the photograph is ever removed from the mat, it can still be identified.
I do not number and have issues with the artificiality of limited editions, so avoid those (you know, make it appear more valuable than it is because it's "limited" - that is until another run is done at a slightly different size which is totally acceptable from a marketing point of view, albeit deceitful - but that's another forum post altogether!).
Really, photographers should be signing their work in the same way watercolourists do - on the front within the work itself - but for some reason it is frowned upon (perhaps it makes us look like we are trying to be painters, I dunno
I also market each matted/framed work as an original photograph, trying never to use the word "print". Although we call them prints, to me each one is a finished and original photograph. I think it is important that photographers push this concept. After all, these are not lithographs run off a hundred or a thousand at a time (although they could be). Nor are they simply knock-offs of an original work - they are photographs!