1. Most helmets have the brand name on the front.
2. Some helmets have a very helpful sticker inside saying "Front."
3. Virtually all helmets have the nape straps (rear straps) anchored at the rear. So the rear will be the end where two straps come almost together at the rim, or even join at the rim. When the helmet is correctly on your head the furthest forward strap should come just in front of your ear and almost straight up to the helmet. If you have a strap coming around the side and angling forward across your cheek, you probably have the helmet on backwards.
4. If your helmet has a stabilizer, that is the rear. All helmet stabilizers are in the rear. There may be an adjustor on the stabilizer strap.
5. The elongated "aero" style helmets are all made with the longer part toward the rear.