  BMS symmetries have been attracting a great deal of interest in recent years.
Originally discovered as being the symmetries of asymptotically flat spacetime
geometries at null infinity in General Relativity, BMS symmetries have also
been shown to exist for free field theories over Minkowski spacetime. In
wanting to better understand their status and the underlying reasons for their
existence, this work proposes a general rationale towards identifying all
possible global symmetries of a free field theory over Minkowski spacetime, by
allowing the corresponding conserved generators not to be necessarily spatially
local in phase space since fields and their conjugate momenta are intrinsically
spatially non local physical entities. As a preliminary towards a separate
study of the role of asymptotic states for BMS symmetries in an unbounded
Minkowski spacetime, the present discussion focuses first onto a 2+1
dimensional free scalar field theory in a bounded spatial domain with the
topology of a disk and an arbitrary radial Robin boundary condition. The
complete set of global symmetries of that system, most of which are dynamical
symmetries but include as well those generated by the local total energy and
angular-momentum of the field, is thereby identified.
