Back in the days when I was on check in (about nine years ago), certain codes were used to alert the security search point if we thought a passenger may require to be more thoroughly searched. Another one I seem to remember was a code for the crew which we wrote on the piece of the boarding card the crew inspects, for instance if they were rude at check in then a code would be written so the crew would be wary of them boarding.
As I said this was a little while ago !
regards,