US DOT placard for Class 2.3, with the legend "Poison Gas".
<a href="https://en.wikipedia.org/wiki/United_States_Department_of_Transportation" class="extiw" title="w:United States Department of Transportation">United States Department of Transportation</a>
2004
<a rel="nofollow" class="external free" href="http://www.cpuc.ca.gov/NR/rdonlyres/DD44FF8C-BBC7-4825-9DC6-157A0D850D22/0/HazardousMaterialsInspections.pdf">http://www.cpuc.ca.gov/NR/rdonlyres/DD44FF8C-BBC7-4825-9DC6-157A0D850D22/0/HazardousMaterialsInspections.pdf</a> &amp; "<a rel="nofollow" class="external text" href="http://hazmat.dot.gov/pubs/erg/erg2004.pdf">Emergency Response Guidebook</a>." U.S. Department of Transportation, 2004, pages 16-17.