45-70!
You have an original Lincoln signature? I'm green with envy!
Here's what I would.
Call up the Smithsoneum museum in D.C., tell them that you you have a document that looks 100% authentic with a Lincoln signature, and ask them to put you in contact with their resident Lincoln expert. They either have a curator on their staff who is an absolute expert, or they have one that is a constant consultant who is an expert as well.
Call him/her up and tell em what you've got. Then send them a photocopy.
After they look at the copy, ask if you can fly out to D.C. to meet with them, with the original, and have them confirm the authenticity of the original. I'm sure they will. They will probably write a letter for you as well.
With this provinence in hand, you will have a very valuable piece of history.
If Chicago or Southern Illinois is closer, then I'm willing to bet that the Fields Museum in Chicago could do the same for your, or an official "Lincoln Society" in Sprinfield.
These curators live and die for this stuff. The discovery of a brand new authentic signature for them can be the discovery of a lifetime. They often publish articles about the new find, which increases their reputation and the value of your paper.
Please don't just sit on this valuable treasure. Something might happen to it. Go forth, authenticate it, reveal it to the World, and then and only then think about taking it to auction. The auction house is where you end up, not where you start.
Hope this helps.
Mannyrock
