The phrase "a powerful indicator" is correct and usable in written English.
It can be used when discussing something that serves as a strong sign or signal of a particular condition or trend.
Example: "The increase in sales figures is a powerful indicator of the company's growth potential."
Alternatives: "a strong sign" or "a significant marker."
Mumbai will forever be associated with cinema - but the story of how Bollywood's home has rescued its film festival through people-power is a powerful indicator of just important that bond is to the city.
The findings reported in all five papers indicate that online visual representations of female genitalia can be a powerful indicator of socially desirable and undesirable genital characteristics.
"It is a powerful indicator of where America will end up on politics, culture, family life.
Our city council re-election victory in Seattle, Washington, this fall is a powerful indicator of the prevailing mood.
The study is a powerful indicator of the importance of planning for retirement, no matter how much money you make.
If it holds true, this could be a powerful indicator that Indonesia's significant investments in forest protection are paying off.
That has never happened in the history of polling, and is a powerful indicator of these polls' internal validity.
More than a dozen studies since the late 1990's have suggested that elevated levels of the protein may be a powerful indicator of heart disease.
The smelt problem was a powerful indicator of the environmental fallout from the delta's water system, which was constructed over 50 years ago for a far smaller population.
The fact that you worked full-time for two years before moving into regular employment may also be a powerful indicator that you were really an employee.
They exist at the top of the marine food chain, which makes them a powerful indicator of the overall health of those ecosystems.
