Traffic signs makes our daily life safe since they prevent accidents on the road from happening. You don't see a traffic sign, where there are lots of accidents do happen. Some car owners might not follow it, but it is still important for the law abiding citizen, so tehy can avoid colliding with other vehicles.
In this game, you put where the signs should be. If you put the sign in the wrong place then ou can always remove it. You can also see the simulation being played in the computer. You know what is wrong and change it, before you even start the "run" button.