are not people named gig who post on message boards. They are unique, limited edition prints that are used to promote bands and concerts
Most posters are created either by screen printing (liquid emulsion technique) or by printing from a computer. The most amazing thing about gig posters is the time and skill required to create one. Various artists have gained notoriety with their skills, and amazingly they see little or no profit from this art. (Although some sell their prints on eBay for reasonable prices). A great place to start looking at gig posters is at http://www.gigposters.com. Be sure to check out some of the Deerhoof and Dead Meadow posters. Amazing stuff.