That's a trick...a fan conspiracy!
Not really, but there's a rubber plug hidden in that shallow recess under the sticker. On some fans, it's very hard to see, but just poke it with something sharp and you'll feel that it's made of rubber.
After the plug is removed, you can carefully pry out the plastic or metal circlip (like a washer with a split in the side to make it a 'c' shape). Once the clip is out, the blade assembly will come right off. Carefull to watch for extra parts...some fans have tiny little wave washers on the center shaft that are almost impossible to find once dropped, and Murphy will make it roll under the center of the nearest immoveable object.
Happy Modding!, and Welcome to the Forums!