South can relay with 4♦ over 4♣ to find out the location of the controls. South can sign off over 3♥ without asking with a terrible minimum 1♣ hand. If N pulls 5♣, the agreement is probably that 5♦ would show 0 or 2 of the top spades and a lot of quacks or some reason for questioning S stopping at 5♣ (over which 5♥ would continue to ask, with no real space to get much and everything else would be to play), but there is some chance a "naturalish" 5♠ pull might make more sense.
Edited to correct that 1♥ shows 4+ spades, not 5+ spades.
This post has been edited by Mbodell: 2012-May-20, 01:18