A method to distinguish between ASS and BSS magnetic fields based on a small amount of data has been proposed by Sofue et al. (1985). Basically, the RM distribution seen along the major axis of the galaxy can be symmetric with respect to the galaxy nucleus for BSS fields, and antisymmetric for ASS fields. A second method to distinguish between ASS and BSS magnetic fields, by analysing the polarization position angle as a function of azimuth angle, has been proposed by Sokoloff et al. (1992).
A small majority of spiral galaxies hosts an ASS magnetic field pattern, while a sizeable minority of spiral galaxies has a BSS magnetic field pattern (e.g., Ruzmaikin et al. 1985). Five examples of a unique or a predominant ASS magnetic fields in galaxies are: IC342 (e.g., Krause et al. 1989a), M31 (e.g., Beck et al. 1989), NGC253 (e.g., Beck et al. 1994b), NGC6946 (e.g., Ehle and Beck, 1993), the Milky Way (e.g., Vallée 1991b; Vallée 1996). Examples of probable or possible BSS magnetic fields in galaxies are: M81 (e.g., Krause et al., 1989b), M33 (e.g., Buczilowski & Beck 1991), M51 (e.g., Neininger 1992; Berkhuijsen et al. 1997), M83 (e.g., Neininger et al., 1993), NGC2903 (e.g., Sofue et al., 1986). More examples of ASS and BSS magnetic fields can be found in the Tables 2 and 3 of the review by Beck et al. (1996).