Here is a good idea! I think it is a visually very powerful and easy to implement feature:
It is simply, make the staff comments have a different color from the rest of the users in the community.
For example, users with the rank administrator, editor, author, would have the color blue in their comments. And users with a collaborator rank would have the color green in their comments.
The color would depend on the WordPress rank, and this feature will be on the posts comments, forums, Buddy Press activity, BP messages…
It could be done through a simple plugin, or code in the theme. With plug-in, administrators could select the colors.
It would be simple to do and very powerful for the community. By this way, the moderators and staff of the web can be distinguished very well.