  Clusters of galaxies produce negative features at wavelengths $\lambda >
1.25$ mm in CMB maps, by means of the thermal SZ effect, while point radio
sources produce positive peaks. This fact implies that a distribution of
unresolved SZ clusters could be detected using the negative asymmetry
introduced in the odd-moments of the brightness map (skewness and higher), or
in the probability distribution function (PDF) for the fluctuations, once the
map has been filtered in order to remove the contribution from primordial CMB
fluctuations from large scales. This property provides a consistency check to
the recent detections from CBI and BIMA experiments of an excess of power at
small angular scales, in order to confirm that they are produced by a
distribution of unresolved SZ clusters. However it will require at least 1.5 -
2 times more observing time than detection of corresponding power signal. This
approach could also be used with the data of the planned SZ experiments (e.g.
ACT, AMI, AMIBA, APEX, 8 m South Pole telescope).
