Actually, intensely radioactive sources can glow. One of the reasons the Goiania accident was so bad, was that children were fascinated with the glow and wanted to play with the material:

http://www.answers.com/topic/goi-nia-accident
"The two attempted to further open the casing, but were unable to. However, they did manage to break the iridium window, which allowed them to see the cesium chloride emitting a deep blue light. The light was caused by some process involving the radioactivity of the source. The exact mechanism by which the light is generated was not known at the time when the IAEA report was written, it is now thought that the blue light is caused by the immense energy being released by the cesium exciting electrons on surrounding air molecules, and as they drop back down to their regular orbitals they emit light. This blue light has been observed at Oak Ridge during the disencapsulation of a 137Cs source in 1988. The light is thought to be either fluorescence or Cherenkov radiation associated with the absorption of moisture by the source. It is stated in the IAEA report that further research work is being undertaken at Oak Ridge to establish the nature of this glow."

@cooper

Actually, unless grandma gained unlawful entry to the home and was posing a physical threat to the residents, that law wouldn't apply.