  In gravitational microlensing, binary systems may act as lenses or sources.
Identifying lens binarity is generally easy especially in events characterized
by caustic crossing since the resulting light curve exhibits strong deviations
from smooth single-lensing light curve. On the contrary, light curves with
minor deviations from a Paczy\'nski behaviour do not allow one to identify the
source binarity. A consequence of the gravitational microlensing is the shift
of the position of the multiple image centroid with respect to the source star
location - the so called astrometric microlensing signal. When the astrometric
signal is considered, the presence of a binary source manifests with a path
that largely differs from that expected for single-source events. Here, we
investigate the astrometric signatures of binary sources taking into account
their orbital motion and the parallax effect due to the Earth motion, which
turn out not to be negligible in most cases. We also show that considering the
above-mentioned effects is important in the analysis of astrometric data in
order to correctly estimate the lens-event parameters.
