...And that Snell sticker is usually affixed to the inside of the helmet, UNDERNEATH the lining, and the sticker is printed on shiny material with real faint ink so it's hard to read unless you're outside in the sun and you know what you're looking for. There's regular printing that says regular stuff -- the "M2000" (also the 1995) is in faint colored ink and overlays the regular print.
I've inspected quite a few helmets and speak here from experience. If it don't got a Snell 95 or 00, I don't let you race. Simple enough, hey?
There ARE other safety certification standards and rating agencies, and they may use other parameters for testing, which parameters may or may not yield equivalent safety compared to Snell -- but SCTA/BNI/USFRA/ECTA recognise only Snell, so that's what you need. You can go to the Snell Foundation website and find a list of all helmets (manufacturer, model, even size) that have been granted Snell certification. Try that to see if your Simpson is okay (if you can't find the sticker). If no sticker but the model IS listed you can try bringing a copy of the approval from the Snell site -- an inspector may allow that end-run around "no sticker inside the helmet".