RCW 9.41.120: Firearms as loan security.

No person other than a duly licensed dealer shall make any loan secured by a mortgage, deposit or pledge of a pistol. Any licensed dealer receiving a pistol as a deposit or pledge for a loan shall keep such records and make such reports as are provided by law for pawnbrokers and secondhand dealers in cities of the first class. A duly licensed dealer may mortgage any pistol or stock of pistols but shall not deposit or pledge the same with any other person.