How can you tell the kind of kind of front passing by just observing the weather?

There are several different types of fronts, a warm front and a cold front. What these fronts do mainly is effect the temperature, the one that normally brings the rain is the cold front, because the cold air is colliding with the warm air already in place.

When a cold front passes over, it lowers the temperature, here's a picture of what this front looks like on a weather map:

When a warm front passes over, it warms the temperature, but when a cold front comes through right after that, it can spark some severe weather, here's a picture on what this front looks like on a weather map: