FIG. 1 shows a perspective view of my design for a curling iron;

FIG. 2 shows a top view thereof;

FIG. 3 shows a bottom view thereof;

FIG. 4 shows a right side view thereof;

FIG. 5 shows a left side view thereof;

FIG. 6 shows a front end view thereof;

FIG. 7 shows a rear end view thereof; and,

FIG. 8 shows a right side view of the design in an opened position.

The broken lines showing the bristles and cord are for illustrative purposes only; and form no part of the claimed design.