If there were too little, inflation would tend to fall below it. To put this same notion in different terms, the risk of having too much, or too little, liquidity in our domestic economy is essentially the same risk that is posed by future inflation being higher or lower than the target.
The key indicators of macroeconomic liquidity, in terms of price, are the policy interest rates and the term structure of interest rates paid by borrowers. In terms of quantity, the key indicators are the growth of monetary and credit aggregates and the state of credit conditions more generally.