A fun litmus test for it would be to de-trend S&P500 to its individual components and to identify and rank contributions of all 500 stocks. But that alone would not get it a job at Rentec or the NSA.

Unlike most commercial & medical applications where signals are stationary with white (uncorrelated) noise, the NSA & Rentec mostly deal with non-stationary signals with regime changes and correlated noise, which can't be denoised without loss of information.

The idea is not so much to predict the next stock price tick or to decipher an intercepted signal (most likely encrypted anyways), but rather to detect "regime changes", ie quickest detection of a change of pattern in non-stationary signals. Then the detected pattern is matched to known trading patterns for a particular stock or to the expected spy activities.