You will use these tokens if you are playing a role variant that uses the Goblin Infestation rules, and you are playing on the hardest difficulty. In this case, when you encounter an Ambush, you will draw a Monster card and read its Ambush text, which sometimes refers to the tokens.
Agreed, thanks from me as well. I'm building a pnp and have been trying to figure out what these are used for. At least I got to read the Goblin rules a couple more times while I searched for the answer.