/3GB is very confusing. Leew is right. It's very important to use this switch since otherwise you may get memory fragmentation.
However, you should also use the /userva switch as per http://support.microsoft.com/kb/815372/en-us
This video shows how to quickly and easily add an email signature for all users on Exchange 2016. The resulting signature is applied on a server level by Exchange Online.
The email signature template has been downloaded from: