The ornamental design for a mountingstanchion with offsetluminaire, as shown and described.
FIG. 1 is a top, front, and right side perspective view of a mounting stanchion with offset luminaire, showing our new design;
FIG. 2 is top, rear, and left side perspective view thereof
FIG. 3 is a right side elevation view thereof;
FIG. 4 is a front elevational view thereof; and,
FIG. 5 is a top plan view thereof.
The broken line disclosure in the views is understood to be of various portions of the article in which the claimed design is embodied, but which forms no part of the claimed design.