Refusing to check in is technically compliance with the sign.

Could it be that they do see a lot of people actually forgetting to check-in even though they have the closed gates?

@stucchimax How can you _forget_ to check in if there is a gate? If you forget, the gate will stay closed and you will not get in. If you tailgate someone or jump over the gate or abuse the emergency button, that's a conscious fare avoidance, not forgetting.

You would be amazed at how many people do tailgate without even realising it.