We investigated the shear interferograms that are produced by superpositions of two vortex beams. When the ratio of the amplitudes of the vortex modes is not too dissimilar (ratio less than 0.6 or greater than 1.7) the interferograms contain an array of vortex signatures that can be decoded. The signature of a vortex in shear interferograms consists of linked forks that reveal the sign and magnitude of the topological charge of the vortex. The distribution of vortices in a superposition of two modes is related to the topological charges of the component modes. Thus, the shear pattern of a composite mode can be deciphered to obtain the topological charge of the component beams and their relative amplitude. This method works for diffracting beams such as Laguerre-Gauss (of radial order zero) and other similar types of modes, such as hypergeometric-Gaussian beams.