The sign-singular measure analysis is a new tool to investigate the scaling features of signals which oscillate in sign on an arbitrarily fine scale. In this work, we apply this new tool to the magnetic fluctuations observed before, during, and after tail current disruption (CD). The analysis shows that sign-singularity is a genuine feature of the magnetic fluctuations in the near-tail region, and that the character of the sign-singularity changes during CD. Different values of the sign-singularity scaling index, named the cancellation exponent &kgr;, are obtained for periods before, during and after the CD. This change of the cancellation exponent is indicative of a reorganization phenomenon, occurring during CD. The results are discussed in connection with magnetospheric substorm onset as well as in the framework of self-organized criticality and 2nd phase order transition. ¿ 1999 American Geophysical Union