The latest ibus-gnome3 + gnome-shell can show a special symbol char on ibus
status icon by ibus engine.
The symbol can be defined in engine's /usr/share/ibus/component/*.xml .

Now ibus-anthy-1.2.6-3 has a symbol char and the similar fix is needed for
major ibus engines.

% grep symbol /usr/share/ibus/component/anthy.xml
   <symbol>&#x3042;</symbol>

The following patch is the example:
http://pkgs.fedoraproject.org/gitweb/?p=ibus-anthy.git;a=blob_plain;f=ibus-anthy-xx-icon-symbol.patch
http://pkgs.fedoraproject.org/gitweb/?p=ibus-hangul.git;a=blob_plain;f=ibus-hangul-xx-icon-symbol.patch

(Note: probably you don't need hotkeys tag since your engine would need Control
+ Space only for the trigger)