...And stick an old ticket to them(e.g. from the garbage). This will make people belief that the system works.
An art concept to recapture public spaces, restricted by admission prices. What about building a bracket system, where we can share our bought tickets for the underground, museums or parking spaces. So we all would have to pay less. This extends our possibilities in public space. The idea is simple: after using your ticket, stick it to a bracket instead of throwing it to the refuse bin. If you have to buy a ticket, instead, take the ticket, archived by someone else.
Step 1: Brackets are the "servers"
These selfmade brackets could be attached to every ticket selling automat. They hold someone's used ticket, which is still valid. Take it!