Dropbox is running, and syncing, but it is complaining that I need to move the sync location. I set up a suitable folder but I have to get my little mouse arrow on the tray icon to tell dropbox where that folder is and I cannot get it to appear. I uninstalled and reinstalled it from the software center. I updated my computer.
dropbox stop && dbus-launch dropbox start which did indeed stop and relaunch it, but did not make the tray icon appear.
dropbox stop followed by
.dropbox-dist/dropboxd also stopped and restarted Dropbox but still no indicator.
dropbox stop && DBUS_SESSION_BUS_ADDRESS="" dropbox start worked great, too. It stopped it and restarted it but ... no indicator.
This question covers some of the same territory Dropbox works but no icon shows in the panel but the OP there is using Xubuntu 14.04 and used the download package from the Dropbox site. They also haven't tried any of the above recommendations (mostly found in the Dropbox Forums.)
How to fix missing Dropbox tray icon? covers the same territory but the issue in that question turned out to be installing the package downloaded from Dropbox, rather than from the Software Center. I installed from the software center.