Saved or not?

A New Mac Tip Every Day
"This is something that isn't well known but it is so useful. When you have a document loaded in any Mac application, you can quickly see if it is saved or not. The red button used to close a window has more use than it looks at first. It actually has a dark red dot in the middle when a document is not saved and a lighter red when it is. In an application that the save feature doesn't apply, it is always the lighter red color."