The letters A, B, and O are disappearing from signs and billboards around the world, as companies drop the letters associated with blood types from their names. It’s all part of an ad campaign from NHS Blood and Transplant and the PR agency Engine Group to encourage blood donations, Mashable reports.

Companies like Google, Santander, and Microsoft have dropped the letters and shared images on social media with the hashtag #MissingType. In total, the campaign includes companies in 21 countries, including the United States, portions of the UK, Australia, Singapore, and South Africa. Several landmarks, including the “I amsterdam” sign in the Netherlands and the “Toronto” sign in Canada have also dropped the letters.

The campaign launches at a moment when blood donations are on the decline. Over the last decade, donations from first-timers in England have dropped about 24 percent, according to the NHS. The organization hopes that by highlighting the need for donations using popular brands, people will be reminded what a difference their A's, B's, and O's can make.

The campaign runs through August 21, so keep your eyes peeled for missing type on social media and on signs around your neighborhood. You can also support the campaign by dropping the letters A, B, and O from your social media handles and, of course, by heading over to your local blood bank to donate.

[h/t Mashable]