The ornamental design for a pop-up sprinkler head, as shown and described.
FIG. 1 is a top front perspective view of a pop-up sprinkler head, shown in use;
FIG. 2 is a top front perspective view of the pop-up sprinkler head;
FIG. 3 is a front elevation view of the pop-up sprinkler head; the rear elevation view, the right side elevation view, and the left side elevation view being mirror images thereof;
FIG. 4 is a top elevation view of the pop-up sprinkler head; and,
FIG. 5 is a bottom elevation view of the pop-up sprinkler head.
The broken lines shown in the drawings illustrate portions of the pop-up sprinkler head that form no part of the claimed design.