It should be written as "come in, Central". "Come in" just is a greeting. "Central" here is an entity or callsign using the radio communication custom. "Situation" means problem.

This seems to be an extract from a conversation between a police officer and at least two other people. His companion and a motorist. He is talking about working on Christmas to his companion. And then notices the motorist doing something wrong (Get a load of this guy). He then calls his base (come in central) to notify them of a potential problem ( a situation). The next sentence (B) is the officer talking to a motorist asking for the licence and registration papers.

When the American astronauts went to the moon, they sent back this message to Mission Control [central headquarters] in Houston, Texas: "HOUSTON, WE'VE HAD A PROBLEM."