If there's one thing about living in California, is you get ot know your way around quakes pretty good. Without a doubt it's their heightened sences that tips them off first. Most earthquakes that rouse me outa my bed in the middle of the night I wake up to about 10-20 seconds before the quake will actualy hit. Sometimes my pet is already on it and is very awake and aware, sometimes me and my pet wake up at the same time 10-20 seconds before impact with that dreadful gut feeling of knowing what's about to hit. There is a very prominent low rumbling noise as the shockwaves move twords your location, and it's an awefuly distinctive rumble if you've experienced it a few times. Best way I can describe it is that someone is firing up a saturn5 rocket a mile under the surface. The sound just eminates everywhere from the ground and you can sence the inbound energy that's about to hit.
Other tell-tale signs anyone can sence in a metropolitan area before any shaking hits is power tranformers blowing out. If it's night-time and the shaking is strong enough, the night sky will brilliantly flash a few seconds before the shaking will hit you. This is because power tranformers will explode/spark when a strong shake hits them and if they have some power still running through them. It perfectly times/ques the sparks/flash on those live transformers in unison as the shockwave aproaches you, creating a visible and very clean and quick flash in the sky before the shaking hits you.
The scariest quakes seem to me to be the ones that happen while I'm working outside and a quake or aftershocks hits. That pre-rumbling noise will start up in the distance and start to get louder, while at the same time if you happen to have a bit of a view, you can see the earth rolling and distant structures/features shaking/vibrating as the quake/waves aproaches you, but the quake still hasnt actually reached you yet. It's like you can see it coming and you know exactly when you're going to get hit. The thing is though that the visual your seeing seems to protray more severe damage/shaking than what it actually will be. A 3.5+ can look very intimidating, but I'd hate to see a 6.0+ coming at me.