  Starting from the groupoid approach to Schwinger's picture of Quantum
Mechanics, a proposal for the description of symmetries in this framework is
advanced.It is shown that, given a groupoid $G\rightrightarrows \Omega$
associated with a (quantum) system, there are two possible descriptions of its
symmetries, one "microscopic", the other one "global".The microscopic point of
view leads to the introduction of an additional layer over the grupoid $G$,
giving rise to a suitable algebraic structure of 2-groupoid.On the other hand,
taking advantage of the notion of group of bisections of a given groupoid, the
global perspective allows to construct a group of symmetries out of a
2-groupoid.The latter notion allows to introduce an analog of the Wigner's
theorem for quantum symmetries in the groupoid approach to Quantum Mechanics.
