The ornamental design for a baby on boardwristband, as shown and described.
FIG. 1 is a perspective view of a baby on board wristband showing my new design; For ease of illustration the text has been omitted,
FIG. 2 is a perspective view thereof; and,
FIG. 3 is a top plan view thereof.
The automobile and other structure shown in broken lines in FIG. 1 represents environmental features that are not part of the design sought to be patented.