DOT-PHMSA has made available a searchable mobile application for both iOS and Android platforms to assist shippers, carriers, and other stakeholders to quickly access information regarding hazardous materials markings, labels and placards. Of course, they quickly say "This application is intended for general guidance only and should not be used to determine compliance with 49 CFR, Parts 100-185. " which presumably even they don't know what the right answers are., but it is better than nothing.
Then download the app here:
The latest version of the Hazardous Materials Markings, Labeling and Placarding Guide includes the following changes: