The polarisation of the light encodes information on unresolved geometries and magnetic fields since it is produced when there is a break of the spherical symmetry in the object that emits it. In particular, in the presence of a global magnetic field over a stellar surface, the polarisation signals depend on the orientation of the magnetic field with respect to the line of sight and on the geometry of the scattering event. Then, a perfect cancellation of linear polarisation signals when averaging the stellar disc is very unlikely. We consider the possibility of diagnosing the global field of the Sun (and of other stars) from the observation of linearly polarised light. The solar-SONG instrument performs synoptic spectroscopy of the Sun as a star. By upgrading the instrument with polarimetric capabilities we could measure for the first time the intrinsic field strength of the solar global dipole and check recent claims that the solar global field is inclined with respect to the solar rotation axis.