Paul (t206collector on here) has assembled probably the definitive reference to early Pre-War signed cards at his website:
http://www.signedt206.com
It’s loaded with scans of amazing signed Pre-War cards. As for 19th century signed cards, I know I’ve seen a back signed Connie Mack N172 and a Hugh Duffy N300. If he doesn’t have images of those two I can dig them up somewhere.
Edit: Also I’ve been traveling for work a lot this month and if I didn’t get back to you I received the Deportivo Noble a while back and meant to thank you for the great card. Happy collecting Phil!