The only signs that are in the shape of a pentagon are found in:

The pentagon-shaped signs are specifically designated for use in school zones. This shape is unique to these signs; it serves to alert drivers that they are approaching an area where children may be present, and extra caution is necessary. School zone signs are often accompanied by additional elements, like flashing lights or reduced speed limits, to further emphasize safety in these areas. The use of a distinctive shape helps drivers quickly recognize the importance of the sign and react appropriately, ensuring the safety of children who may be crossing roads or waiting for school buses. Other shapes and forms are used in road signs for construction zones, passing zones, and no passing zones, but only school zone signs utilize the pentagon shape.