expression.NewMessageSignature
expression Required. An expression that returns an Email object.
Remarks
When setting this property, you must use the name of an e-mail signature that you have created in the E-mail Options dialog box, available from the General tab of the Options dialog box (Tools menu).
Example
This example changes the signature Word appends to new outgoing e-mail messages.
With Application.EmailOptions.EmailSignature
.NewMessageSignature = "Signature1"
End With