Some letters will again be "missing" from some signage this week, but it is not a case of vandalism.

More than 50 organisations are removing blood type letters A, B and O from their signage and branding materials, in support of a campaign to encourage blood donation.

This is an increase from the 33 organisations that supported last year's inaugural campaign.

The Missing Type Campaign is a joint initiative by the Singapore Red Cross (SRC) and the Health Sciences Authority (HSA) to increase the number of blood donors in the country. It will be held from today to Sunday.

The need to increase the pool of blood donors comes with the rise in blood usage, which is growing at a rate of 3 per cent to 5 per cent a year, the SRC and HSA said in a press statement yesterday.

Currently, the blood donor pool stands at 1.87 per cent of Singapore's resident population.

Singapore's ageing population adds to the urgency of the situation, as some 600 regular donors stop donating every year due to age-related illnesses, said the statement.

SRC secretary-general Benjamin William, said: "By bringing the Missing Type Campaign back, we hope that it not only serves as a reminder for donors to make a second trip to the blood bank, but also acts as a catalyst to start the conversation about blood donation and motivate new donors to action."

Notable local brands such as Carousell, The Soup Spoon and BreadTalk - involving its BreadTalk IHQ hub in Paya Lebar - are participating in the campaign for the first time. The Botanic Gardens is removing the blood type letters from its physical signage, while Swiss Cottage Secondary School in Bukit Batok is covering the letters on its physical signage.

Ms Joanna Leng, 27, a project manager at an events company, believes the campaign will raise awareness about blood donation.

"This is a rather interesting concept to encourage people to donate blood. It makes people curious and want to learn the reason behind those missing letters," she said.

Individuals and organisations can participate by taking a photo of themselves with their ABO-omitted names, and posting it on their social media pages, with the caption, "I've dropped my (As/Bs/Os) to support the #MissingTypeSG campaign. You can do the same too and help spread the word about blood donation: redcross.sg/miss ingtypesg".

More information on the campaign can be found at redcross.sg/missingtypesg