expression.ReplyMessageSignature
expression Required. An expression that returns an EmailSignature 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 e-mail message replies.
With Application.EmailOptions.EmailSignature
.ReplyMessageSignature = "Reply2"
End With