If an airfield isn't marked (like the majority of the farm strips about the place), there is a high probability that you neither know what they are called, or know where they are. This should lead to the obvious conclusion that any broadcast from someone operating from such a field will have zero meaning to you, even if you see a farm strip AND see someone takeoff from it, any radio call will still be meaningless to you
So common sense applies.
Anyone departing from a strip unlikely to be known would broadcast something like:
ALL STATIONS, ABC C172 taxying at a private strip 22 miles east of Ballarat, departing to the North below 5000.
It's not rocket science ...