The phrase "subtle indication" is correct and usable in written English.
You can use it to describe a sign, gesture, or action that is not clear or obvious. For example, "The driver gave a subtle indication that he was about to turn left."
Yet always there is a tinge of sadness, a subtle indication of a tormented soul.
It was a subtle indication of D'Antoni fitting his playbook to his personnel.
Ladders, rocks, and fallen tree trunks are lined with white paint in the game, a subtle indication that they can be climbed or traversed.
There is, perhaps, one other subtle indication of a writer knowingly book-ending his career or, at least, one sequence of novels.
Before he left, Dolan gave a strong endorsement of the roster as currently constructed — a subtle indication that he perhaps was not convinced that D'Antoni was getting the most out of it.
Iraq watchers believe that a popular protest movement calling on Abadi to better handle public services and government corruption is a subtle indication that Iraqis want to beat back Iranian influence in their country.
But there were subtle indications of an arduous exchange.
But Upton stripped out a lot of Gorky's subtle indications of character and status and distorted the Russian context.
But there are subtle indications: In 2005 Cheryl Porter, 17, drew the car in which she and her family escaped.
Given that Mr. Bush is the president's brother, public controversies in Florida tend to be closely watched for even subtle indications of involvement from Washington.
In fact, there seem to be subtle indications that various "goods" that High-G.D.P. Man consumes should, as some economists put it, be characterized as "bads".
