Part of the publicity of big events are the creation of posters and flyers. Aside from word-of-mouth marketing, I believe this is one of the oldest ways of promoting something. However, these kinds of practices have their limitations.
Let's say that it is this way for posters. Ethical attitude will tell you that you should not go ahead and stick posters in places that you do not own, unless you got the permission of the owner or you it was allotted by the government as a venue for posting promotional materials. I guess there's no problem with that.
But getting permission to post on walls is something difficult to do, primarily because it leaves a lot of mess after the poster is removed. You know what I mean. This is similar to posters in one's room wherein the paint peels off once the poster is taken off. Which wall owner with a sane mind would want his/her wall's paint to be peeled off? That's where the problem arises.
I can think of two solutions to solve the problem. First is to not post posters on walls at all. You can instead purchase a bulletin board where you can pin your posters. This won't only lessen the hassle of asking permissions. It will also allow you to have a portable posting place.
The second one, and I believe it's the cheaper one (at least in the short term) is to buy poster tapes that peel off easily. They are widely available in the market though they are more expensive than ordinary tapes--but if posting in that particular place will improve your event's publicity, why not spare the additional money?
All UPSable
