The ornamental design for a seahorse shower head, as shown and described.
FIG. 1 is a front-right-top perspective view of a seahorse shower head showing my new design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken line showing of a seahorse shower head is included for the purpose of illustrating portions of the article and forms no part of the claimed design.