Do you have a photo in mind? And are you speaking about an individual frog or a species of frog? I might be able to help you out :)
It is definitely NOT a cane toad. It is some type of ranid frog, however the photo is too dark. Pig frog or river frog are my best guesses.
Dave is correct. But there is another device called a frog that is used to rerail cars after a minor derailment. There is the "Buddha" frog and the "butterfly" frog, often seen hanging on the sides of locomotive trucks.