Kurapika reserves his middle finger for the Troupe. When he flicks them off, magical chains come and tie them up cuz he's into that stuff.
…Actually, I'm not sure if he has specific fingers reserved for the Troupe, just that his binding chains are only supposed to be used on them.
Edit: It does look like Kurapika uses his middle finger on Uvogin (:P), but I'm pretty sure it isn't limited to only that finger. One's a dousing rod though.
You mean chain jail how about Emperor Time more explanation please