I claim the ornamental design for a button assembly, as shown and described.
FIG. 1 is a top perspective view of a button assembly of the present disclosure;
FIG. 2 is a front elevational view of the button assembly of FIG. 1;
FIG. 3 is a rear elevational view of the button assembly of FIG. 1;
FIG. 4 is a side elevational view of the button assembly of FIG. 1;
FIG. 5 is a top plan view of the button assembly of FIG. 1; and,
FIG. 6 is a bottom plan view of the button assembly of FIG. 1.
The dash-dash broken line showing of the environment is for illustrative purpose only and forms no part of the claimed design. The dash-dot broken lines define the bounds of the claimed design and form no part thereof.