My six-year-old has a bluish/grayish mark on her forehead that has gotten darker over the past three days. At first, we thouggt it was pencil smeared on her skin. The, it appeared to be slight bruising. Today, it looks like a line or vein that isn't going away. She said it doesn't bother her until we touch it, but feels sore to the touch. She said she cannot remember being injured or hitting her head. What could it be? We are concerned it might be something we should be paying attention to.