After installing a Microsoft update for Outlook, the Encrypt/Sign buttons not available in Outlook 2010 for Symantec Encryption Desktop in order to trigger encryption and signing functionality.
A recent Microsoft update causes Outlook 2010 to always start in Safe Mode, thus disabling the Encrypt/Sign plug-ins for Symantec Encryption Desktop for email encryption.
In order to restore the encrypt\sign buttons for Symantec Encryption Desktop within Outlook, uninstall the update referenced in the following Microsoft article:
https://support.microsoft.com/en-us/kb/3114560