Revealing mistake: The roller coaster used for the Devil's Flight is really the Corkscrew at Playland in Vancouver, where all three movies were filmed. If you look during the opening credits, you can see the name "Corkscrew" up in the lights above the coaster. After this, it says Devil's Flight during the rest of the roller coaster scenes.
Revealing mistake: At the end of the film where Wendy is stuck on the track, she looks back at everybody that died. At the right side of the screen, right in front of the camera, you can see a dead girl blink.
Answer: A sickle is a harvesting tool with a crescent-shaped blade (with the sharp edge on the inside) as seen on the old USSR flag (along with a hammer). It's a reference to Death, who is most often seen dressed in black cloak with a scythe. On rare occasions Death has a sickle, but more often it's people confusing the two tools or thinking the words are synonymous. Plus, it's easier for some people to say "sickle" than "scythe." Ian is saying Death is on the ride.
Bishop73