I claim, the ornamental design for ignition plug for internal combustion engine, as shown and described.
FIG. 1 is a perspective view of ignition plug for internal combustion engine, showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is a front elevation view thereof in a typical usage environment.
The broken line portion of FIG. 8 is included to show an unclaimed internal combustion engine usage environment and forms no part of the claimed design.