Customizing Object based action icon

Hi Experts,

The question is pretty straightforward: how does one create a custom icon for an object base action? I know the drill for workflow based ones, at least I know the scmessage class for them, but object based? Where? How?

In details: I've made a custom action for the probsummary object named Subscribe: displayed on the tray.

I'd really like to localize this message (create translations for it) and put a 16x16 icon before it (only for webtier of course)

Thanks in advance,

Dávid