Is it really necessary to say "URGENT"?  I doubt anyone will respond any faster/sooner.  

Anyway:

bind_meta_app will do * + a char to do an action.  So *# could be hangup.

You could listen to DTMF events over ESL and do whatever action you want.  Keep in mind you should have a maximum time duration between the first a second char.  That way, if I hit # 1s into the call and then again 5min into the call you don't hangup on me.