The volatility index, Williams vix fix developed by Larry Williams, is a well-known index for finding market bottoms. It describes how much the current low price statistically deviates from the maximum within a given look-back period.
The inverse can be formulated by considering "how much the current high value statistically deviates from the minimum within a given look-back period." This transformation equates Vix_Fix_inverse. This indicator can be used for finding market tops, and therefore, is a good signal for a timing for taking a short position.