We present an analysis of the second solar spectrum, as plotted in graphical form in the three volumes of the atlas “The Second Solar Spectrum”, in the wavelength range between 3160 Å and 6995 Å. All the strongest positive linear polarization signals produced by atomic spectral lines are identified, and their amplitudes are listed, along with the most relevant spectroscopic properties of the lines. The various signals are divided into five classes according to the shape of their Q/I profiles. Three empirical rules are formulated from the analysis of the amplitude and shape of the various signals, and of the spectroscopic properties of the spectral lines. Tables 1 and 2 are only available in electronic form at http://www.aanda.org