Signs communicate laws all drivers must understand and obey.

The answer is regulatory signs. The term regulatory sign defines a range of signs that are used to specify or emphasize traffic laws, rules or requirements which apply either at all times or at indicated times or places upon a street or highway, the neglect of which may constitute a violation, or signs in general that regulate public behavior in places open to the public. Traffic signs are the best example for this kind of signs. It is intended to instruct road users on what they must or should do (or not do) under a certain set of conditions. Other types may be signs positioned on streets and in parking lots having to do with parking, signs in public parks and on beaches or on or in architectural facilities prohibiting specific types of activities. 

the earthquake in haiti was a magnitude of 7.0 according to the u.s geological survey yet the smaller earthquake in haiti killed more than 200,000 and left more than 1.2 million people homeless. the chile earthquake was a magnitude of 8.8 and 500 times more stronger but chile's earthquake only injured 712 people.