The ornamental design for a surface pattern representing a musical stave on a chair seat, as shown and described.
FIG. 1 is a top plan view of a surface pattern representing a musical stave on a chair seat showing my new design.
FIG. 2 is a right side elevational view thereof, the left side being a mirror image.
FIG. 3 is a perspective view of a surface pattern representing a musical stave on a chair seat. The chair shown in broken lines is for illustrative purposes only and forms no part of the claimed design.
The front, rear and underside of the chair seat are unornamented.