If you plan to hang a vinyl banner where the sun will shine through it at some point during the day, be sure to use vinyl with a blockout layer. This will ensure that the light will not 'bleed through' your sign to make it difficult, or impossible to read.
It's hard to imagine, but the thin blockout layer is between the 'front' and 'back' layers of vinyl. In addition to improving redability, the slightly thicker vinyl banner also installs better and has less curl on the corners.
All of the vinyl banners on GardenCenterMarketing.com, including single sided, have this blockout layer.