The checkmark was removed because, being an HTML page, the checkmark is an image and is referenced relatively. If you move the sign-in sheet file, the checkmarks become broken images. So I removed the image references to avoid this issue entirely.
I actually ran across this just yesterday and thought that it is a little difficult to distinguish between the 'yes' and 'no' at a quick glance. My thought was to add a preference that allowed you to specify what you want for "yes" and what you want for "no". That way you could, for example, use "yes" and "", making the distinction more visible. Or, return to what was used before by using "<img src=../images/checkSmall.gif>" and "".