The ornamental design for a sign, as shown and described.
FIG. 1 is an isometric view of a sign showing a design according to the present disclosure.
FIG. 2 is a front view of the design of FIG. 1.
FIG. 3 is an end view of the design of FIG. 1, with the opposing end view and the top and bottom views being identical thereto; and,
FIG. 4 is a rear view of the design of FIG. 1.
The broken line showing of elements on the sign illustrate portions of the sign and form no part of the claimed design. The edges and back of the sign form no part of the claimed design.