The ornamental design for a snow plow blade, as shown and described.
FIG. 1 is a perspective view of a snow plow blade, showing my new design, the broken lines showing a support frame are for illustrative purposes only and form no part of the claimed design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a left side elevational view thereof, the other side being a mirror image;
FIG. 4 is a rear elevational view thereof;
FIG. 5 is a top plan view thereof;
FIG. 6 is a bottom plan view thereof.