Don't do it. (C-C-C-Combo Breaker!) Just kidding do it. I tried it at school but it got taken off within an hour. Hopefully you'll do better.
My country has these boards were political parties (Companies are allowed too, but During elections it's full o Government propoganda.) can freely paste on Advertisements and such. If your country has them as well. 1. Wait for elections. 2. Overwrite every flyer with This edited to be up-to-date 3.??? 4.PROFIT!