Caltrans road sign SR63 ("NO IDLING All Buses and Commercial Vehicles")
<a href="https://en.wikipedia.org/wiki/California_Department_of_Transportation" class="extiw" title="en:California Department of Transportation">California Department of Transportation (Caltrans)</a>
Sign and specifications: <a rel="nofollow" class="external free" href="http://www.dot.ca.gov/hq/traffops/engineering/control-devices/specs/SR63.pdf">http://www.dot.ca.gov/hq/traffops/engineering/control-devices/specs/SR63.pdf</a>