This app was mentioned in 4 comments, with an average of 2.00 upvotes
I'm not affiliated with this app, but I use it. It's interesting to see what gets hauled around in trucks.
Cargo Decoder
https://play.google.com/store/apps/details?id=com.strategiesinsoftware.erg
I keep an app called Cargo Decoder installed: https://play.google.com/store/apps/details?id=com.strategiesinsoftware.erg
You can enter the four digit codes on any of those cargo ID placardss and it will tell you what it is. Tapping on the substance brings up information about it and precautions/dangers/response info.
There are other tabs for generic placards, and other relevant information like emergency numbers and the like.
So far I've only ever used it for curiosity to identify what's in a truck I'm passing, but it's great to have the info if I need it.
There are apps for that. Kinda fun to decode trucks on a long road trip.
This app will tell you exactly what those numbers represent.