Emails on my Exchange 2010 server do not have a SCL value or X-MS-Exchange-Organization-SCL: in the email header.
Does anyone know how to enable this so I can filter spam from my users
You can set both SCL and headers using Transport Rules.
In the Exchange Management Console, there are under Organization Configuration -> Hub Transport.
For setting SCL, in the Actions step, you should flag set the spam confidence level to value. For headers, the flag is set header with value.
You can use this cmdlet in the Exchange Management Shell.
Set-ContentFilterConfig -SCLQuarantineEnabled $true -SCLRejectEnabled $true -SCLDeleteEnabled $true -SCLQuarantineThreshold 5 -SCLRejectThreshold 6 -SCLDeleteThreshold 8 -QuarantineMailbox SpamQuarantineMailbox@contoso.com -RejectionResponse "Message rejected due to content restrictions" -BypassedRecipients email@example.com,firstname.lastname@example.org