Vehicle Theft Risk

What is the Police saying here? As I drove up this MSCP there was an earlier poster warning about car theft. After I had parked my car, I saw this poster even before I could make my way out of the building.

I usually do not park here but the other car park was full.

Not a good sign. I don't remember seeing these posters before. This car park is surrounded by low income housing. I have noticed police patrol cars in the vicinity pretty often too. Guess this is a reason for their frequent visits.