Posters are very flexible as they can be put anywhere regardless of the place. You should always get permission to display them but apart from that they can be posted on walls, windows, public washroom doors, street displays, bulletin boards and more. They can be placed almost anywhere for people to see. This makes the material very accessible to people. How many times have you stopped to look at one while walking or just passing through? If one can get your customers´ attention, they are also bound to read the message, making it one of the most effective promotional materials around.