Possible Clues:

• It's observed on Oct. 24
• Oct. 24 observance
• Annual observance for a global organization, for short
• Annual Oct. 24th observance
• 10/24 celebration of global cooperation
• International observance in 20-Down, informally
• Annual Oct. 24 observance
• Oct. 24, 1947 declaration
• Oct. 24
• Oct. 24, every year