It really depends on how the customer wants to setup the signage solution:
1. Is it a separate network ?
2. Will it have access to sensitive data ?
3. Should it allow employees to upload content to it ?
Off the top of my head I would have the following security measures as a baseline:
SSL, SFTP (for file transfer), AD authentication service, HTTPS access only
With more information it would be possible to recommend further security measures.
Thanks Aviad Cohen