This might have already been suggested - I haven't the time right now to check the whole thread - but I had a thought today as I did my walkaround.
On the engines there is a pictogram showing the minimum safe distance from the (running) engine intake one should be. On the A321 with V2500 engines I flew today it says no closer than 15' or 5 meters with engine at idle. However, the warning is on the engine itself which is not much use to ramp workers, because if they are close enough to read the warning they are probably too close for safety.
What is needed is some sort of semi-circular marking on the underneath and sides of the fuselage behind the nose-wheel, aft of which one should never go if the engines are running. Pushback crew would be able to clearly see the line from the front and sides of the aircraft and be told never to go further backwards towards running engines than that line.
This might improve safety but would not prevent a problem if the aircraft moved forwards before the crews were clear. I can't remember which, but I have been to an airfield where the headset person places a chock in front of the nose wheel after pushback until they are fully disconnected, and as they are walking clear, they pull the chock with them, thus preventing the aircraft running forwards until they are safe.