‘Writing on the wall’
When someone says that the “writing is on the wall,” they’re referring to the fact that a situation is very clearly and inevitably going to become unpleasant or difficult. The phrase is Biblical in origin, coming from the story of Belshazzar’s feast in the Book of Daniel.
In the story, King Belshazzar is feasting and drinking from sacred vessels looted from a temple when a disembodied hand appears and writes on the wall a warning that God has numbered the days of the kingdom because of Belshazzar’s impiety. Even after Daniel interprets this message for him, Belshezzar ignores the warning, leading to his downfall.