99% of the time all you need to do is make sure you clicked "Publish" and make sure you refresh your Gmail.
If this didn't help, maybe the permissions you gave WiseStamp were lost.
Simply follow these steps (must be done by the Domain Admin who installed WiseStamp):
1 - go to google.com/a/yourdomain.com
2 - click the "Marketplace apps" icon
3 - click "Email signature marketing tools - WiseStamp"
4 - click "Data access approval needed" and then "Grant data access" (see image)
That's it - the permission is now on and you can continue updating your company signature.