We see posters in store windows, stapled to lamp-posts, tacked up on bulletin boards, put up in libraries and living rooms, taped to to walls and windows (providing of course we are not talking about flyers!) published in books, and occasionally we see excellent posters framed and exhibited.
Posters are of course a 2-dimensional medium, and rarely is it, that a poster has not been reproduced in multiple numbers. This is not a one-of-a-kind art form.
Posters have a particular beauty in that they 'most always combine a picture, an illustration, a painting, or a photograph, with text of some description. Script. A Font. A Hand. An Alphabet. Calligraphy. This text can run right across the picture, or placed at the top, or there at the bottom, and in various sizes and/or colors, depending on the impact desired. This is not a medium that is rarely seen, nor which requires the viewer to enter a museum to see.
However the most charming posters - the originals - are only visible in the museums, and were done by Toulouse LaTrec during the middle of the 19th century, I believe it was in France: all his lettering was filled in and done by hand, and has a lovely elegant quality.