  We introduce a new technique to detect the discrete temperature steps that
cosmic strings might have left in the cosmic microwave background (CMB)
anisotropy map. The technique provides a validity test on the pattern search of
cosmic strings that could serve as the groundwork for future pattern searches.
The detecting power of the technique is only constrained by two unavoidable
features of CMB data: (1) the finite pixelization of the sky map and (2) the
Gaussian fluctuation from instrumental noise and primordial anisotropy. We set
the upper limit on the cosmic string parameter as $G\mu\lesssim 3.7\times
10^{-6}$ at the 95% confidence level (CL) and find that the amplitude of the
temperature step has to be greater than $44\mu K$ in order to be detected for
the {\it{Wilkinson Microwave Anisotropy Probe (WMAP)}} 3 year data.
