The markings on the grip straps of the police Lugers were not unit markings, but represented the town or district they were assigned to.
The sear safety is above the side plate on your pistol. It is a spring that was attached to the left side of the receiver with a pin that blocks the sear bar when the side plate is removed. Your first picture shows the sear safety on the left side of the receiver, with a round head pin at the back, and extending up over the side plate.
Your pistol should have a hold open. The hold open is actuated by the follower button on the magazine. As the last round in the magazine is chambered, the follower button rides up against the hold open, raising it and locking the slide back when the pistol fires the last round.