  In the last decades, noncommutative spacetimes and their deformed
relativistic symmetries have usually been studied in the context of field
theory, replacing the ordinary Minkowski background with an algebra of
noncommutative coordinates. However, spacetime noncommutativity can also be
introduced into single-particle covariant quantum mechanics, replacing the
commuting operators representing the particle's spacetime coordinates with
noncommuting ones. In this paper we provide a full characterization of a wide
class of physically sensible single-particle noncommutative spacetime models
and the associated deformed relativistic symmetries. In particular, we prove
that they can all be obtained from the standard Minkowski model and the usual
Poincar\'e transformations via a suitable change of variables. Contrary to
previous studies, we find that spacetime noncommutativity does not affect the
dispersion relation of a relativistic quantum particle, but only the
transformation properties of its spacetime coordinates under translations and
Lorentz transformations.
