The phrase "a sharp warning of" is correct and usable in written English.
It can be used to indicate a strong or clear indication of a potential danger or problem.
Example: "The sudden drop in temperature served as a sharp warning of the approaching storm."
Alternatives: "a clear indication of" or "a strong alert to".
The chief inspector of schools has delivered a sharp warning to the government that the opening of more grammar schools would be "a profoundly retrograde step" that would damage the prospects of disadvantaged children.
Former Vice President Al Gore (D) issued a sharp warning to lawmakers challenging the validity of global climate change in an interview with Australia's Fairfax Media this week.
The disclosure sends a sharp warning to the CIA to stay out of Lebanon, with Hezbollah suggesting it could have captured the officers at any time.
For the avoidance of doubt, as Thomas Cromwell might say, and before the silliness goes any further, I'd like to clarify that I have never issued a "sharp warning" to the BBC about their treatment of Wolf Hall for TV (Even Holbein would recognise it: Mantel hails BBC's Wolf Hall, 12 December).
The US justice department also issued a sharp warning to the election boards in the relevant counties of Beaufort, Moore and Cumberland.
She issued a sharp warning to the BBC earlier this year not to dumb down and oversimplify history in its adaptation of her bestselling novel Wolf Hall.
But it already serves as a sharp warning to U.S. companies doing business overseas.
And they offered a sharp warning to politicians who threaten the law's protections.
The Fox News host Tucker Carlson, a vigorous defender of President Trump, shocked many viewers recently with a sharp warning about the dangers of market capitalism.
While the sanctions are not imminent, the list amounts to a sharp warning, covering a range of products far more sweeping than any other retaliatory action proposed in recent memory.
