Comment # 21 on bug 1156501 from Dr. Werner Fink

The XDG values for the sessions:

local display:

  printenv | grep -E 'XDG_(CURRENT|SESSION)'
  XDG_SESSION_PATH=/org/freedesktop/DisplayManager/Session10
  XDG_SESSION_DESKTOP=KDE
  XDG_SESSION_TYPE=x11
  XDG_CURRENT_DESKTOP=FVWM
  XDG_SESSION_CLASS=user
  XDG_SESSION_ID=11

ssh without X11 forwarding

  printenv | grep -E 'XDG_(CURRENT|SESSION)'
  XDG_SESSION_ID=63
  XDG_SESSION_TYPE=tty
  XDG_SESSION_CLASS=user

and with X11 forwarding

  printenv | grep -E 'XDG_(CURRENT|SESSION)'
  XDG_SESSION_ID=64
  XDG_SESSION_TYPE=tty
  XDG_SESSION_CLASS=user

last but not least a VNC display:

  printenv | grep -E 'XDG_(CURRENT|SESSION)'
  XDG_SESSION_TYPE=unspecified
  XDG_SESSION_CLASS=background
  XDG_SESSION_COOKIE=noether
  XDG_SESSION_ID=62

... is there a way to overwrite session type and class within the vnc
service/socket units?