It's not obvious but if you hover over the the System: Version: section of the header it will be listed in the pop-up. 
Hey all, Where in the ME4012 UI can I find the service tag number?  I am 500 miles away from the front of the machine. You would think this would be an obvious thing, it's all over the place on the iDrac UI, but the ME4 series do not post it in any obvious way. -Dan
Service Tag on ME4012