Add a META tag to the HTML generated for each web-UI page that identfies the version of the DSpace source running on the site. This lets administrators and developers tell at a glance what their test servers are running, and curious visitors see what version of DSpace is behind a production site.
The change is very simple and automated in action. Maven is already doing property-substitution on the dspace.cfg file, so let it plug in the verison of the "dspace" project (under group "org.dspace"), which should always be the same as the released or snapshot project for the source tree. From there it's a simple matter of putting it in a pageMeta element for the XMLUI.
NOTE: This still needs a volunteer to either implement it for JSPUI or point out the most efficient way to do – I'll be happy to code and test but I don't know the JSPUI well enough to spot the most effective place to put a META tag that goes on every page.