I thought 'I bet Vice have a documentary on this', and actually a perfunctory search didn't turn one up, but there's this, from about two years ago:
And it turns out they have just banned public wearing of gang patches today!
Ban on public display of gang insignia is part of a wider crackdown on gangs that some experts say could infringe on rights while doing nothing to cut gang membership
www.theguardian.com
New Zealand’s gangs will need to hide their gang patches or face prosecution after a new law banning gang insignia in public came into force on Thursday – a move critics believe could risk breaching the Bill of Rights and do little to reduce gang membership.
At midnight, it became illegal for gang members to display signs, symbols or patches – large insignia sewn on to jackets, for example – anywhere in public. This includes displaying insignia on their clothing or vehicles.
Breaches of the ban carry a sentence of up to six months imprisonment or a $5,000 fine, and insignia would have to be forfeited and destroyed.
Three minutes after the ban came into effect, a Mongrel Mob member based in Hastings was arrested for displaying a large Mongrel Mob sign on the dashboard of his car, the police confirmed to the Guardian. He was issued a summons to appear in court and the sign was confiscated, police said.