Acrobat X Signature

I am woking with Acrobat Pro 10.1.7 on mac OS 10.6.8.

I made a new ink signature by scanning my signture and importing it in to Acrobat > Preferences > Security > New. That worked and I can see that signature under Preferences. When I try to sign a document, however, I cannot find that new signature when I go to Tools Panel > Sign and Certify > Sign Document. Why not?

Marc