No Animal Sign
From the Super Mario Wiki
No Animal Signs are objects featured in Donkey Kong Country 2 and 3 and their handheld counterparts, Donkey Kong Land 2 and III. They are located in levels with an Animal Friend, and their only purpose is to prevent them from crossing it, oftentimes at the end of a level.
In its Donkey Kong Country appearances, the corresponding Animal Friend is depicted on the No Animal Sign, with a red no symbol over it. In the Donkey Kong Land series, every sign only depicts the no symbol.
The Animal Friend disappears if the Kongs ride it past a No Animal Sign, otherwise, if it emerged from an Animal Barrel, it transforms back into the Kongs. The Kongs are usually rewarded with an item, such as an Extra Life Balloon. The rewards usually improve based on the level difficulty. There are a few instances where crossing a No Animal Sign reveals a DK Coin.
In Donkey Kong Country 3, crossing a No Animal Sign may turn the Animal Friend into an object that leads to a collectible, such as a Steel Keg meant to throw behind a Koin, or even a Bonus Barrel. Nibbla also has its own sign, but unlike the other Animal Friends, it stops at the sign and does not move past it.
In Donkey Kong Land III, No Animal Signs no longer spawn rewards when crossed. Some levels have an Animal Friend without a corresponding No Animal Sign. This means that the Animal Friend can reach and activate the Level Flag, but it is still unable to access the following level.
No Animal Signs do not appear in the first Donkey Kong Country, so DK and Diddy can finish a level with their mounted Animal Friend. However, it cannot proceed to the next level with the Kongs. This is also the case in its modern sequels, Donkey Kong Country Returns and Donkey Kong Country: Tropical Freeze.
While No Animal Signs do not appear in Donkey Kong 64, Rambi and Enguarde transform back into their respective Kong, DK and Lanky, if they go outside their intended region. Before this occurs, a red no symbol displays on-screen, accompanied by a menacing laugh.