Have the same set up as Kalros.

Except that it is a round-robin key.

Tank targets mob A.
I press my hotkey, which sends that keybind to Toon A.
Toon A - FTL Assists tank, sets target as their Focus, and announces in /Party their Focus.

Tank targets mob B
Next press of the key, Toon B does the same.

Resets back to the first step, after I believe 10 seconds without anything being assigned.

Then a key to /Cast Whatever @Focus.



Was thinking of raid icons.
But you cannot place them on hostile players.
And I want the system to work for everyone.

Could go with them, and something to suppress the error message.
That would work.
Or alternatively, just go separate keys for the marking -- although my toons don't have issue with improper assisting or being on the right target.