Detailed observations of the second solar spectrum have shown a complex phenomenology whose detailed interpretation is still in a preliminary phase. The only certain thing is that the observed polarization is due to the phenomenon of resonance scattering. It is well known that such polarization can be strongly modified by the presence of a magnetic field through the so-called Hanle effect. It then follows that the second solar spectrum is, at least potentially, a fundamental instrument for diagnosing the intensity and topology of the weak magnetic fields lying in the higher layers of the solar atmosphere. Obviously, to fully exploit such potential, it is absolutely necessary to arrive at the correct theoretical interpretation, a task that has been revealed to involve many difficulties. We present an analysis of the second solar spectrum, carried out with the aim of investigating its general properties. The most interesting results concern an empirical classification of the wide variety of polarization signals that are observed, and the formulation of three empirical laws describing a series of properties common to the strongest signals.