Having just returned from an overseas trip (USA) where the Security Screesning was excessive to say the least I can see that the passenger behaviour depends largely on the attitude of the security officers. Firstly, passengers have to get to the airport hours ahead of scheduled departure times to allow for the security process and then be directed/ordered by a security officer instead of REQUESTED can start the ball rolling. This situation gets progressively worse when a passenger just wants to get on with the trip and not get undressed at a security point (take off shoes and belt etc
and during this time the departure time is upon him/her.
It may help a little if the union concentrated on the correct personnel for this thankless job as some personality could go a long way and from my observation, some were devoid of this.
Notices in airports may moderately assist but most passengers won't/don't read signs.