Caravaner Gort:
Yes, the Berserker Guild uses a special message plate.
It usually gets mixed with the food monsters love to eat and is consumed. Since the material the plate is made from is indigestible, the next team is able to collect the plate by killing the monsters near the route the convoy took.
If we assume that the convoy took the planned route, then we may get the plate from the Road Scavenger in Death Pass.