Why is there a warning sticker on all football helmets?

The National Operating Committee on Standards for Athletic Equipment (NOCSAE) has developed standards for football helmet certification to minimize the risk of skull fractures and brain bleeds. Athletes must be provided with quality protective equipment, especially football helmets. All helmets must have NOCSAE certification. Although these helmets ensure safety, it must be noted that helmets cannot prevent all head injuries, and ultimately, even if used correctly, the athlete is still playing at his or her own risk. (This answer provided for NATA by the Saint Louis University Athletic Training Education Program.)