I ran in to this issue too. In my case it was for NetApp LUNs.
Here's what to do. Right-click the disk and select 'copy identifier to clipboard':
Browse to http://codebeautify.org/hex-string-converter , paste the identifier you copied and click Convert:
The result (the decoded string) will be the serial number of the NetApp LUN. The command 'lun show -v' on the NetApp will show serial numbers.
Hope this helps, but to be honest if you just name your datastores with a proper name you need never concern yourself with naa numbers anyway