LOL.

The M stands for Motorcycle. SA is special application. The difference is that the foam and lining of a SA helmet is fire retardant. The 2000, 2005, etc. is the year in which the certification was filed.

All helmets are subjected to testing by Snell Labs, iirc. Snell then certifies the helmet. Here's the web site for Snell, if you want to read up about the testing procedures.