  The possible experimentally observable signal in momentum space for the
critical point, which is free from the contamination of statistical
fluctuations, is discussed. It is shown that the higher order scaled moment of
transverse momentum can serve as an appropriate signal for this point, provided
the transverse momentum distribution has a sudden change when energy increases
passing through the critical point. A 2-D percolation model with a linear
temperature gradient is constructed to check this suggestion. A sudden change
of third order scaled moment of transverse momentum is successfully observed.
