How do you suggest teacher's and administrators respond to student graffitti about "Bombs" and "Shootings?"

Our high school is getting more than one a week and our administrators seem to overreact in my opinion. Do you think evacuations and lock downs every time a hint of violence is mentioned is appropriate? It seems to encourage copy cats and the students are having a great time missing cl with lots of laughing during the lock downs and such. It is really quite a game to them and they are enjoying watching the adults get frustrated and annoyed. Suggestions?