The ornamental design for a warningsiren, as shown and described.
FIG. 1 is a perspective side view of a warning siren showing my new design;
FIG. 2 is a right side elevational view thereof with the left side being a mirror image thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a rear elevational view thereof;
FIG. 5 is a top plan view thereof; and,
FIG. 6 is a bottom plan view thereof.
The broken line showing of mounting holes is included for the purpose of illustrating portions of the “article” and forms no part of the claimed design.