We identify high-density regions of supercluster size in high-resolution n-body simulations of a representative volume of three cold dark matter universes. By assuming that (1) the density and peculiar velocities of baryons trace those of the dark matter and that (2) the temperature of plasma is proportional to the velocity dispersion of the dark matter particles in regions where the crossing times are smaller than the supercluster free-fall time, we investigate how the thermal motions of electrons in the intracluster medium and the peculiar velocity of clusters can affect the secondary anisotropies in the cosmic microwave background (CMB). We show that the thermal effect dominates the kinematic effect and that the largest thermal decrements are associated with the most massive clusters in superclusters. Thus, searching for the presence of two or more nearby large CMB decrements represents a viable strategy for identifying superclusters at cosmological distances. Moreover, maps of the kinematic effect in superclusters are characterized by neighboring large peaks of opposite signs. These peaks can be as high as approximately 10 µK at the arcminute angular resolution. The simultaneous pointed observations of superclusters in the millimeter and submillimeter bands combined with the upcoming sensitive CMB experiments can separate the thermal effect contributions from the kinematic effect contributions and can constrain the evolution of the velocity field in large overdense regions.