How To Tell The Bad Aliens from the Good Guys

Himself and I have been enjoying Enterprise (once you get past the sucky opening theme song).

You know how in Westerns you can tell the good guys from the bad guys because the good guys wear a white hat sometimes?

 Well, Himself noticed in Enterprise, the bad aliens have ridges on their foreheads. Also, spikes, nodules or antenna.

So any protruberant feature is a dead give away for a bad guy. Sometimes.