I believe the main point of signing with pencil is that it's much easier to prove it's an original, if it's signed in pencil. A print signed in ink could just as easily have been /printed/ with that signature in ink. At least, that's my understanding.
I would also be extremely leery of putting a sticker on the back of your artwork. It might claim to be archival, but what about the adhesive? Also (depending on the paper used), it might pucker or bow in the area of the sticker as the humidity increases and decreases. Maybe I'm just paranoid.
I just write it on the back bottom edge in pencil:
(C) 2000 Jenny de la Cruz, http://www.pixelscapes.com