Before Kali River rapids opened at the Animal Kingdom, Imagineers had a slightly different name in store for the ride. Originally the plan was to call it Tiger River Run. The reason that it was changed at the last minute was to improve clarity. Potentially guests could have been disappointed with the lack of tigers on the attraction. The could have also got confused with the Maharajah Jungle Trek, on which you do actually see tigers.
The design work had clearly already been in place for the signage and you can see the remnants of the tiger signage on the current attraction.
Thanks to Rich Oswald for the photographs.