There are no symptoms of deficient demand, like deflation.
What about disinflation? Is there something special about zero (nope)?:
This is a graph of the year over year percentage change in the CPI less food and energy, but it doesn't much matter which measure of underlying price trends is examined, this "symptom of deficient demand" is very evident. And that's not the only sign that demand is insufficient. It takes effort not to see them.