Try this:
 Code:
$objSysInfo = CreateObject("ADSystemInfo")
$strUser 	= $objSysInfo.UserName
$objUser	= GetObject("LDAP://" + $strUser)

$strName 	= $objUser.FullName
$strSN 		= $objUser.sn
$strmobile 	= $objUser.mobile
$strTitle 	= $objUser.Title
$strDepartment 	= $objUser.Department
$strCompany 	= $objUser.Company
$strPhone 	= $objUser.telephoneNumber
$strGivenName 	= $objUser.givenname
$strMail 	= $objUser.mail

$objWord 	= CreateObject("Word.Application")

$objDoc 	= $objWord.Documents.Add()
$objSelection = $objWord.Selection

$objEmailOptions = $objWord.EmailOptions
$objSignatureObject = $objEmailOptions.EmailSignature
$objSignatureEntries = $objSignatureObject.EmailSignatureEntries

$objSelection.TypeText("Kind Regards,")
$objSelection.TypeParagraph()
$objSelection.TypeParagraph()
$objSelection.TypeText($strGivenName + " " + $strSN)
$objSelection.TypeParagraph()
$objSelection.TypeText($strTitle)
$objSelection.TypeParagraph()
$objSelection.TypeParagraph()
;objSelection.TypeText($strDepartment)
;objSelection.TypeParagraph()
$objSelection.TypeText($strCompany)
$objSelection.TypeParagraph()
$objSelection.TypeText("P: " + $strPhone)
$objSelection.TypeParagraph()
$objSelection.TypeText("M: " + $strmobile)
$objSelection.TypeParagraph()
$objSelection.TypeText($strmail)
 
$objSelection = $objDoc.Range()

[color:#CC0000]$objSignatureEntries.Add("AD Signature", $objSelection)[/color]
$objSignatureObject.NewMessageSignature = "AD Signature"
$objSignatureObject.ReplyMessageSignature = "AD Signature"

$objDoc.Saved = 1
$objWord.Quit


If it doesn't work try removing the [color] /[color] tags