Each signal line can be shown as a linear superposition of periodic (sinusoidal) components
with different periods (frequencies) and amplitudes. Roughly, the indicator shows those
components. It strongly depends on the probing window and changes (recalculates) after each tick.
E.g., you can see the set of frequencies showing whether the signal is fast or slow-changing, etc.
Sometimes only a small number of leading / strongest components (e.g., 3) can extrapolate
the signal quite well. Another example of that type of indicators is attached (from the site of MQL Service).
I played with it years ago, and it's quite funny, but gives you practically no help how to trade.