From Halopedia, the Halo wiki
Ewww, Sticky is an Achievement in Halo 3: ODST. It is unlocked when the player sticks any enemy with a Plasma Grenade or Spike Grenade 5 times on any Campaign or Firefight level. It is worth 5 Gamerscore.
It is represented by a gold 16-pointed star, with another blue 16-pointed star within, and a blue ball with the number 5 written in it.