The ornamental design for a flagsafetydevice, as shown and described.
FIG. 1 is a perspective view of a flag safety device showing my new design positioned on a vest;
FIG. 2 is a front view of the flag safety device of FIG. 1:
FIG. 3 is a rear view of the flag safety device of FIG. 1;
FIG. 4 is a left-side view of the flag safety device of FIG. 1;
FIG. 5 is a right-side view of the flag safety device of FIG. 1;
FIG. 6 is a top view of the flag safety device of FIG. 1; and,
FIG. 7 is a bottom view of the flag safety device of FIG 1.
The broken lines depicting a vest in FIG. 1 represent environmental subject matter that form no part of the claimed design. The broken lines in FIG. 3 depict portions of the flag safety device that form no part of the claimed design.