Not too relevant for digital signage, but thought you would find this article interesting. Check out PC World Magazine's list of The 25 Worst Tech Products of All Time.
In 1996, there was a product called PointCast that was ranked 12th worst product. PointCast looked like a cluttered digital sign, but was used by individuals on their desktop computers. It was really cool.
The product was very popular and installed by thousands of users for streaming news, sports and other information. The product was supported by advertising revenue. PointCast's bandwidth requirements clogged corporate networks and was soon banned by many businesses. PointCast last broadcast was in 2000. I bet they would be in the digital sign software business today if they were still around.
If anyone has a screenshot of this product - let us know and we'll post it here.