There will be a sticker on the inside of the helmet, behind the padding on some helments. It should be easily visable.
The sticker will be either Brown (M Certification), Orange (SA certification) or Blue (K Certification), along with type and Year... EG: SA2010, SA2005, M2005, M2010, etc.
SA is designed for mutliple impacts; and is recommended if you are driving inside an automotible. A motorcycle helmet is designed for 1 impact, with the premise being; you only will fall off the bike once.
When strapped inside of a car you can hit your head multiple times. If you drive a vehicle with a roll cage; you MUST use a Snell SA helmet for that reason.