The ornamental design for a verticalunistrutstrap, as shown and described.
FIG. 1 is a front perspective view of the vertical unistrut strap, the back view is omitted as it is a mirror image of the front perspective view;
FIG. 2 is a side view;
FIG. 3 is a front view thereof in use; and,
FIG. 4 is a front cross section view thereof in alternate use.
In the drawings, the broken lines depict environmental subject matter only and form no part of the claimed design. The undisclosed portions (top and bottom view) of the article are not shown as they are unornamental.