North Carolina DMV Practice test link below:

THE SHAPE AND COLOR OF SIGNS DIFFERS WITH THE TYPE OF INFORMATION THEY PROVIDE:
You may be asked the color and shape of different types of signs: 

REGULATION SIGNS

WARNING SIGNS

DESTINATION SIGNS

INFORMATIONAL SIGNS
 

The STOP sign 

Stop Sign Law: Come to a full stop, yield the right-of-way to vehicles and pedestrians in or approaching the intersection. Go when it is safe. You must come to a stop before the stop line, if there is one. If not, you must stop before entering the crosswalk. If there is no stop line or crosswalk, you must stop before entering the intersection, at the point nearest the intersection that gives you a view of traffic on the intersecting roadway.

yield 

Regulation signs

Signal Ahead 

YOU MUST BE ABLE TO RECOGNIZE AND KNOW ALL SIGNS. 

REGULATION SIGNS
REGULATION SIGNS  ARE USUALLY WHITE RECTANGLES WITH BLACK LETTERS OR SYMBOLS
 

SOMETIMES THEY MAY USE RED LETTERS OR SYMBOLS
TIP - They are regulating something, your speed, turns, etc.

WARNING SIGNS
 

WARNING SIGNS ARE YELLOW WITH BLACK LETTER/SYMBOLS DIAMOND SHAPE AND SOMETIMES COMBINED WITH A RECTANGULAR "RECOMMENDED SPEED" SIGN 

TIP - They are warning you of conditions ahead.

DESTINATION SIGNS

DESTINATION SIGNS 

GREEN WITH WHITE LETTERING 

SHOWING DISTANCES AND DIRECTIONS TO VARIOUS LOCATIONS 
 

SERVICE SIGNS

SERVICE SIGNS ARE BLUE WITH WHITE LETTERING 

SHOWING LOCATION OF HOSPITALS, GAS AND REST AREAS ETC. 

SOME EXAMPLES ARE: