And an ad campaign is appealing to the public: "Help fill in the gaps."
It's a public awareness campaign spearheaded by the National Health Service in the U.K. The NHS first ran the campaign last year, with the missing letters a mystery at first. The campaign registered more than 30,000 people to donate blood, the organization says.
The New York Blood Center is working with Morgan Stanley, the Hard Rock Cafe and the U.S. Merchant Marine Academy, among other groups, to promote the effort — including in a display in Times Square.
In the U.K., entities and organizations from Microsoft to the City of Manchester are contributing. The Royal Mail even created a special postmark that will be used this week, the NHS says.
The public awareness campaign is necessary because dwindling numbers of new donors make it harder to meet the need for blood, the NHS says. Each year, it says, some existing blood donors become unable to give "for reasons such as ill health, pregnancy or foreign travel," and more than 200,000 new donors are needed to replace them.
The Royal Air Force has lost its A's and O's in support of the NHS Blood and Transplant campaign Missing Type.
Cpl. Steve Buckleyll (RAF)/NHS
The shortage of new donors is a worldwide phenomenon, the health service says. A survey of blood services participating in the Missing Type campaign found the number of first-time donors per year had dropped more than 27 percent between 2005 and 2015.
"We hope that this will be one of the largest public sector campaigns in recent history," Jon Latham, assistant director of marketing and donor services at NHS Blood and Transplant, said in a statement. "We expect to see lots of exciting things happening around the world over the next few days."