Can't remove unknown symbol from menu bar
This is the icon for an old version of Adobe Application Manager or Adobe Updater. It wouldn't show up in the standard Force Quit dialog, so I would recommend the following steps:


Open Activity Monitor, either by searching in Spotlight (Command-Space) or opening it from /Applications/Utilities/Activity Monitor.
Search for "adobe".
Select each relevant result and click the "X" octagon in the top left, then confirm with the Force Quit option.
Reopen Adobe Application Manager or Adobe Updater, and use it to update or uninstall the two pieces of Adobe software which need to be updated.