If you use propane to power your gas grill, or for some other reason you might want to keep an eye out--for a blue-green discoloration on the valve.
If you see that, your propane tank could have been used before in a meth lab. The blue-green discoloration comes from anhydrous ammonia.
If you do come upon a tank like this, the best thing to do is call the police immediately. A tank formerly used to make meth can cause severe damage to the skin, lungs, and even cause a deadly explosion.
Kentucky State Police are warning everyone to check their tanks before they plug them in.
Another way to spot a tank used to make meth is if the tank smells like ammonia.