The ornamental design for a securecap for a syringe, as shown and described.
FIG. 1 is a top perspective view of a secure cap for a syringe showing my new design;
FIG. 2 is a front view thereof, a rear view being a mirror image of the front view;
FIG. 3 is a left side view thereof, a right side view being a mirror image of the left side view;
FIG. 4 is a top plan view thereof;
FIG. 5 is a bottom plan view thereof;
FIG. 6 is a bottom perspective view thereof;
FIG. 7 is a perspective view showing the secure cap in an environment of use with a syringe where the syringe is not inserted into the secure cap; and,
FIG. 8 is a perspective view showing that the secure cap in an environment of use with a syringe where the syringe is inserted into the secure cap.
The broken lines shown in the figures illustrate environmental structures and form no part of the claimed design.