Robbie, there is absolutely zero difference between indicators and the features you derive from LOB snapshots. None. Indicator = feature = independent variable = right-hand-side variable, etc... I also derive features from LOB snapshots for (after winnowing/reduction) input into ML or statistical inference modules.All I'm saying is the people who are using indicators and make money are profitable for other reasons, but not the indicators.
These LOB-derived features may or may not have any forecast ability for, or mutual information with, future returns, but they're all "indicators."