This is how I hang posters in my studio space.
All you need are 3M Command Strips, wooden clothespins, and scissors.
First, cut a Command Strip lengthwise.
Then, remove the red and white backing and place the strip on the clothespin so that the pull tab is hanging from the bottom of the clothespin as shown here.
Remove the black and white ("wall side") backing and affix to the wall. I usually find two clothespins are needed for larger posters. Place the poster inside the grips of the clothespins.
With this method, there's no adhesive on the poster itself. You also have a lot of leeway in repositioning the poster to get it nice and straight without having to reposition the clothespins. And, of course, the clothespins are reusable!
As a bonus, you can also use clothespins at the bottom of a poster to temporarily weigh it down and straighten it out.
Posted May 12 at 7:54 PM while cleaning the studio.