If the email signature does not display after synchronising BrandMail, this could be caused by: 

1. The toolbar not being defaulted. The remedy would be to default the toolbar and the signature will then appear. 

2. Older versions of Microsoft Outlook (e.g. Office 2010), which could display as follows: 

If rebooting the workstation does not solve the problem, please check that all the latest "patches / updates" for Outlook have been installed. 

Ideally, upgrading Outlook to 2013 or 2016 will resolve the problem. 

Please see article on checking your default toolbar for more details.