I read a manga (japanese comics) called "Boys on the Run". In some chapters several characters refers to someone as "the mole", but I don't actually know who is that person. Here is the context: A company made a line of figurine toys for adults, and people refer to "the mole" as the one that designed these toys.
Here are some examples of sentences where the word is used: "But it's really well made. This was definitely made by the mole"; In this case, they are saying that "the mole" made these toys. "Maybe the mole can make this?", In this example, someone is telling other that some toys should be made by "The mole". I do not think it means something like "traitor" because the first sentence I put as example is said by a person that does not belong to the company, so it does not make sense if he is implying they have a traitor.