  Recent observations show that rings and gaps are ubiquitous in protoplanetary
discs. These features are often interpreted as being due to the presence of
planets; however, the effect of planetary migration on the observed morphology
has not been investigated hitherto. In this work we investigate whether
multiwavelength mm/submm observations can detect signatures of planet
migration, using 2D dusty hydrodynamic simulations to model the structures
generated by migrating planets and synthesising ALMA continuum observations at
0.85 and 3 mm. We identify three possible morphologies for a migrating planet:
a slowly migrating planet is associated with a single ring outside the planet's
orbit, a rapidly migrating planet is associated with a single ring inside the
planet's orbit while a planet migrating at intermediate speed generates one
ring on each side of the planet's orbit. We argue that multiwavelength data can
distinguish multiple rings produced by a migrating planet from other scenarios
for creating multiple rings, such as multiple planets or discs with low
viscosity. The signature of migration is that the outer ring has a lower
spectral index, due to larger dust grains being trapped there. Of the recent
ALMA observations revealing protoplanetary discs with multiple rings and gaps,
we suggest that Elias 24 is the best candidate for a planet migrating in the
intermediate speed regime.
