What is the origin of the idiom "the writing is on the wall" and when to use it?

The idiom "the writing is on the wall" is believed to have originated in the Bible, where it was said to have been written on the wall during a feast in ancient Babylon as a warning of impending doom. It is often used to describe a situation where there are clear signals or indications that a situation is about to change or that something is about to happen.