The ornamental design for a displaydevice for an electric bicycle, as shown and described.
FIG. 1 is a perspective view thereof;
FIG. 2 is a bottom plan thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 is a right-side view thereof;
FIG. 5 is a left-side view thereof;
FIG. 6 is a front view thereof; and,
FIG. 7 is a back view thereof.
The evenly dashed-lines represent the remainder of the article and do not form part of the claimed design, are directed to environment, and represent unclaimed subject matter.