People have to look at them
Posters do not have to pay for the space they occupy. Despite any city ordinance or regulation, a poster can be put under the cover of night and speak its message until removed. A bold combination of image and text cannot be ignored by anyone who catches a glimpse of it from the corner of their eye - everyone does a double take automatically at something strange.
Anyone can make and post them
Posters can be made in any quantity from 1-10,000 or more. They can be one of a kind or reproduced in any way an individual has access to- stencil, photocopy, screen print, offset print, computer print, etc. Posters can be put up anywhere and can be made very difficult to remove if it is so desired with the use of adhesive. If a message urgently needs to be spoken, it can be done.
A poster is a catalyst
Posters start people thinking and people who are thinking about things start conversations. A poster can remind someone of an issue that they feel strongly about and help them to cause change. A poster with a strong enough message that is seen by only a few hundred people before it is removed can actually reach a whole city by the buzz it creates.
A poster can be reactionary
Posters can be immediate responses to current issues and events. Their timeliness can build momentum toward change.
A poster is locally relevant
A poster is created for a certain audience in a certain location. Many posters would not be understood outside of their local context because it speaks directly to a certain community.

5 Reasons Why Posters Are Influential
by Dan D Shafer Copyright 1999. All Rights Reserved.