Number systems you over hear on the train on the Metro,?

Question

what are they, and why d they use 10 4, they use it on cops, what is 10 4?

When you waiting for the train the intercom checking nimber between train times.

Answer 1

They are an official verbal short-hand.  Much quicker to say "10-28" than it is to say "Vehicle registration information".

10-4 = Acknowledgement (OK)