The letters O and A went missing from the Northland Age's online masthead and signage from other leading brands around the world in a life-saving bid for blood.
Medical blood collection agencies in 21 countries, including New Zealand, yesterday latched on to a highly successful marketing campaign, called Missing Type, which had its first run in Britain last year.
Global megabrands such as McDonald's, Google, Coca-Cola and Microsoft were among businesses which removed the letters from their websites, Twitter handles and signage to help promote the UK National Health Service's appeal for new blood donors.
More than 30,000 people registered to donate.
The NZ Blood Service received commitments from numerous brands, including Anchor, Pak'nSave, New World and NZME - publisher of the Northland Age, Northern Advocate and New Zealand Herald - to omit the letters yesterday, kicking off the seven-day campaign.
But as part of the top secret move, the brands provided no explanation until this morning, confusing many readers and consumers.
In New Zealand, A and O went into hiding and unlike the UK, B remained on duty.
"We're not going 'B'," said Blood Service chief executive Sam Cliffe.
"The UK have a higher percentage who are B+. Our real need is As and Os."
In New Zealand, 85 per cent of people are A or O, meaning their kind of blood is in greatest demand.
Fewer than four per cent of eligible Kiwis donate blood. The Blood Service has around 110,000 blood donors on its database and about 42,000 people a year receive blood products. Every year around 28,000 drop off the donor registry.
The target of the New Zealand Missing Type campaign is to sign up 10,000 eligible people to become donors.
"We also want to look at getting young donors," said Mr Cliffe.
"If we get them at high school or school-leaving age, often they stay life-long."
The number of active donors has decreased from 128,412 in the 2011 financial year, to 109,158 last year, according to the service's annual report.
In part this reflects changes in the way blood products are used, but that does not eliminate the need for new donors to join up.
Mr Cliffe said fewer whole-blood donors were needed, but rapidly rising demand for products made from plasma - a component of blood comprising mainly water, plus proteins, hormones and clotting factors - meant more plasma-only donors were needed.
To become a plasma-only donor, which carries additional eligibility criteria, new donors must first give a unit of whole blood.
Last year more than 59,000kg of plasma, up from 49,000kg in 2011, was sent to a laboratory in Melbourne for processing into blood products for use in New Zealand.
The NZ Blood Service produced some 112,000 units of red blood cells last year, down from 138,000 in 2011.