It's pretty easy to discern a rear fog lamp from the brake lights.
Usually the rear fog is a SINGLE lamp, installed on the driver's side. For example, the Audi A4 has a setup like the Euro XJ (with fog lamps integrated in to the tail light unit), but only the driver's side fog lamp lights up. Plus, the fog lamp always has a bulb separate from the brake light, so if you had any question about what that light was, you'd see more light when the brakes were applied.
The problem here is that we're used to seeing the stupid, cheap tail light design that most American companies use -- a single bulb that's used for stop, tail, and turn functions. Everything is red, and when it gets bright, you have to think for a second (and look at the other tail light) to see if it's stopping or turning. If they switched to a typical european setup, which has seperate bulbs for each function (and amber turn signals), it would be easier to tell what's going on.
And please, NEVER DRIVE WITH YOUR HAZARDS ON, regardless of the weather. Not only is it illegal in most states, but your turn signals don't work when your hazards are on.