  We report on the a5F-y5F* 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 \AA line
(whose lower and upper levels have Land\'e factors equal to zero), relative to
the rest of the lines in the multiplet, gives direct evidence for the existence
of an 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.
