I attended a Lynnwood Citizen's Academy with my family. It was held in the courtroom above the Lynnwood Police Department. Every night (it started at 7pm), I would go straight to the Police Department window, tell the person/officer that came to the window that I needed to check a firearm. The person would go to the desk, grab a lockbox key, hand it to me and point to the lockbox location. I'd take out my weapon from concealed carry at the lockbox, put it in there, lock it back up and handed the key back to the issuing person.
Pretty straight forward procedure.
If the courtroom you go to doesn't have the same office arrangement as in Lynnwood, just ask the police officer nearest the main entrance where you check your firearm. He or she will direct you to the proper location.