What are these stamps on my icons?

Recently some of the icons on my desktop of my PC running Windows-7 have acquired stamps in the form of a red dot containing a white exclamation point on the center of the bottom edge of the icon. I don't see any information as to why these icons have been marked, looking at properties or opening the files doesn't cause any warnings to appear. Most of the marked files are documents - .doc, .gif, .odt, .pdf, .txt, .odp, .png, .mp4, .ppt, and one is an .exe file. Anyone know what this stamp means? It appeared after we added a new Nvidea card, but seems unlikely that should have anything to do with it.