Board Thread:Support Requests - Getting Technical/@comment-3150645-20170925200832/@comment-27345308-20170925201008

It means the latest active administrator will be the one that appears in wall greetings, per Help:Welcome tool. The welcome tool is a little broken, though, so sometimes users may not get greeted.

You can also set it to  to disable wall greeting messages,   to make it always show as if an administrator greeted a user or to somebody's username to make it always show that user when greeting new users.