NOCSAE, the National Operating Committee on Standards for Athletic Equipment is an organisation that has formed test standards for various sports helmets, face masks and headgear.
If a helmet has been submitted and meets the testing standard then its manufacturer is allowed to put the NOCSAE logo on the item. This is usually moulded into the item at the rear.
For full details visit the NOCSAE web site http://www.nocsae.org
Note: NOCSAE certification will not prevent injuries, it means the item has been tested to a standard.