They tell you where you are, what road you are on, and how to get to where you wish to go.
Many guide signs are rectangular, but some have other shapes as shown for interstate signs.
There are several different kinds of guide signs - route markers, information, destination, distance, and location signs. Zero always starts at the south or west borders where route begins. These roads are going to cross or meet the highway you are using. The numbers on these signs designate specific exits. Look for this sign when you want to park.