If you're going racing --- make sure it has a SA2010 rating (it will have a sticker on it somewhere) or the sanctioning body most likely won't let you wear it.
This is the SCCA 2013 seals of approval requirements....
http://scca.cdn.racersites.com/prod/...ert_decals.pdf
Even at Optima Ultimate Street Car invitational -- and events run by American Street Car Series such as RTTC etc - Tech checks your helmet!