The signatures for Outlook are stored in the folder:
C:\Documents and Settings\username\Application Data\Microsoft\Signatures

Now all you have do to is go to the folder and make a backup of all the files. Each signature will have three associated files (.htm, .txt and a .rtf file).

Simple if you know where to look.

Check out these posts too:

  1. Outlook 2010 – My Experience
  2. Microsoft's Rich Signature (undocumented)
  3. SyncToy v2.0 Beta
  4. See what’s in your Outlook PST file
  5. Software: SyncToy v2.0
  6. Windows Live SkyDrive
  7. How to access Outlook Express Newsgroups from Outlook