Final answer:
The sign that indicates that the road becomes slippery when wet is the 'Slippery When Wet' sign. It warns drivers to exercise caution and reduce their speed on wet roads.
Step-by-step explanation:
The sign that indicates that the road becomes slippery when wet is the one with a wavy line symbolizing water.
This sign is called the 'Slippery When Wet' sign and it warns drivers to exercise caution and reduce their speed when the road is wet or covered in rain, ice, or snow.
The sign is typically yellow or fluorescent yellow-green in color to enhance visibility.
When driving on slippery roads, it is important to maintain a safe following distance, avoid sudden braking or acceleration, and drive at an appropriate speed.