Open remote application window over ssh – X11

You left the office but forgot to leave an application running. An application that requires it’s GUI, you try to open it via ssh but “Error: Can’t open display” prevents you.
Simple fix here, you will kick yourself.
DISPLAY=:0 <command>
for me this translated into
DISPLAY=:0 transmission
What this does is instruct the application to open in display 0, which [...]