"clear warning" is a common phrase used in written English.
For example, you could write: "The doctor gave him a clear warning to stop smoking immediately."
It was a clear warning to the "deviated current".
It was a clear warning, which unfortunately went unheeded.
That should be a clear warning to Mr. Mubarak that his time has passed.
The opinion sounded a clear warning that Congress had better fix the act.
The investigation uncovered a clear warning about Sandusky, then the defensive coordinator for the Nittany Lions.
In Portugal's fate there lies a clear warning for other countries, the United States included.
That would send a clear warning that the United States was ready and willing to act.
Like the packaging around cigarettes, tickets for games like this should come with a clear warning.
They also send a clear warning signal to the authorities that their actions are being observed.
The sensors gave clear warning of a catastrophic explosion, which came two months later.
Tusk issues a clear warning that he wants serious progress at an emergency EU summit.
