Interest shown. How many people are we looking for? Also, an idea for identifying participants: The microchip is linked to the optic berve as well, and projects big fuckoff arrows over the heads of all players. That way it would be something only they could see because it's just an electric signal sent to the brain. Basically an illusion.
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Edit: after thinking more on that, I'd like to expand my idea. The microchip could display a whole HUD on the players' vision, complete with radar, those arrows, vital moniters anything like that.