Outlook: Cannot Insert Multiple Signatures
Microsoft Outlook does not allow more than one signature to be inserted into a message. When a signature is inserted, Outlook remembers the section of the message containing the signature, meaning the signature section is somewhat “special”. When another signature is inserted, the new signature is placed into the section occupied by the previous signature.
This behaviour was changed in Outlook 2010. Previously it was possible to add multiple signatures to a message, which enabled signatures to be used as a type of template or boilerplate. Try Quick Parts instead.