The council said the signs breached local bylaws.
A defended hearing before Judge Keith de Ridder was convened last week, where both parties presented their arguments.
Council lawyer Julian Dawson said the truck was worth $1500 and the cost of impounding it stood at $3270, as at July 30 last year. The council, he said, was entitled to sell the truck and to pursue any shortfall in costs.
Mr Dawson said there had been a history of illegal sign complaints against Mr May since 2005. Despite the council issuing abatement notices and infringement fines, the problem continued.
In his defence, Mr May argued the Signs Control Bylaw 2005 under which his truck was seized was invalid because it was not reviewed in November 2010 - five years after it was made - as directed by the Local Government Act 2002.
When that bylaw was made, authority for making a bylaw governing advertising was vested in Section 684 of the Local Government Act 1974, he said.
However, that section was repealed in 2011 and replaced by section 22AB of the Land Transport Act 1998, he said.
Mr May had also displayed signs on his truck calling for council chief executive Mark Simpson to stand down.
The council is prepared to return the truck upon payment by Mr May of its costs but he is refusing to pay.
He has vowed to fight the matter in court, saying the council's actions in seizing his truck may be unlawful under the Bill of Rights Act.
Judge de Ridder advised both parties to make written submissions before reserving judgment.