When I first bought my CPL at the Snohomish Police station, I missed a sign saying you are not allowed to bring a firearm beyond the front door and I did when I went to buy my CPL and a cop saw me and looked at my 1911 but didn't say anything.
If you were able to just walk in then that sign was placed illegally without regard to the law. Cop didn't say anything because you were the only one that wasn't a criminal present.
Marysville PD has the same sign on their lobby door. I disregarded it, went in, and handed them my application for renewal with check. Had a "detective" come in, stand right behind me, and give me a good look. I turned and did likewise to him. He left and went into the secure area using his key.
The sign really isn't illegal, it just has no legal repercussions as long as you aren't going to any area that isn't open to the public. If a door isn't locked consider what's behind it "open to the public". If you have to go through security, have the door opened for you and you have to be escorted, don't take your firearm with you.
BTW, also went in to pick up my license while carrying and still no issues. For some reason Marysville holds the license for EXACTLY 30 days before they hand it over to you. I asked and was told "Chief's Orders".
