The ornamental design for a label for a bottle, as shown and described.
FIG. 1 is a front view of a label for a bottle showing the new design; and,
FIG. 2 is a top, front perspective view of FIG. 1.
The broken lines depicting the label and parts thereof shown in the drawings are included for the purpose of illustrating environmental structure and form no part of the claimed design. The broken lines depicting the shape of the bottle form no part of the claimed design.