We report on the a5F-y5Fo multiplet of Ti I and its interest for the study of ``turbulent'' magnetic fields in the quiet solar photosphere. In particular, we argue that the sizable scattering polarization signal of the 4536 Å line (whose lower and upper levels have Landé factors equal to zero), relative to the rest of the lines in the multiplet, gives direct evidence for the existence of a ubiquitous, unresolved magnetic field. We cannot determine precisely the strength of the magnetic field, but its very existence is evidenced by the differential Hanle effect technique that this Ti I multiplet provides.