Firearm dealer are required to record and report all pistol sales to the state department of licensing, and the local police or sheriff.
RCW 09.41.110(9)(a) and (b)
What is Firearm Registration?
Most states do not require owners to register their firearms with the police. A few states only require that certain types of firearms maybe registered, such as assault weapons. Registering your firearm involves fingerprinting, recording the gun's serial number, your name, and address.