Once.
Funny story, completely different incident...I was in a mall open carrying when two real city police officers approached me. They politely informed me that the mall was private property and had a policy against firearms. I mentioned that I looked for signs on the doors and didn't see any, but I understood that none were required. They said just cover it up and it won't be a problem, so I put my shirt over the gun. That was it. No asking for a permit or anything.
Buried in the middle of the "Code of Conduct" sign posted inside the doors was the "no firearms" line.
Unfortunately, in Washington state it is the law that if a LEO asks to see your CPL, and you have your CPL in your possession, you must show it to them, whether or not you are carrying a concealed pistol. Of course, if you are not carrying a concealed pistol, there is no requirement to have your CPL in your possession.