The ornamental design for a safetyhelmet, as shown and described.
FIG. 1 is a front, top and right-side perspective view of a safety helmet showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 is a right-side elevational view thereof, the left side being a mirror image; and,
FIG. 5 is a rear elevational view thereof.
The details shown in broken lines form no part of the claimed design. The dot-dash lines represent boundary lines that form no part of the claimed design.