public Map<Integer, String> getSignatures() {
        ensureRunning();
        // Make a copy so callers get an immutable snapshot of the current state.
        return Collections.unmodifiableMap(new HashMap<Integer, String>(signatures));
    }
public Map < Integer , String > getSignatures ( ) { ensureRunning ( ) ; return Collections . unmodifiableMap ( new HashMap < Integer , String > ( signatures ) ) ; }
Get the signatures that have been computed for all tracks currently loaded in any player for which we have
been able to obtain all necessary metadata.

@return the signatures that uniquely identify the tracks loaded in each player

@throws IllegalStateException if the SignatureFinder is not running