  We demonstrate that patterns formed by the current-current correlation
function are landmarks which indicate that spin bipolarons form in doped
antiferromagnets. Holes which constitute a spin bipolaron reside at opposite
ends of a line (string) formed by the defects in the antiferromagnetic spin
background. The string is relatively highly mobile, because the motion of a
hole at its end does not raise extensively the number of defects, provided that
the hole at the other end of the line follows along the same track. Appropriate
coherent combinations of string states realize some irreducible representations
of the point group C_4v. Creep of strings favors d- and p-wave states. Some
more subtle processes decide the symmetry of pairing. The pattern of the
current correlation function, that defines the structure of flux, emerges from
motion of holes at string ends and coherence factors with which string states
appear in the wave function of the bound state. Condensation of bipolarons and
phase coherence between them puts to infinity the correlation length of the
current correlation function and establishes the flux in the system.
