Railroad is signed exactly like train: take both hands, extending the middle and index fingers. Take your dominant hand and rub your two fingers flat, slowly down the same fingers on the non-dominant hand. It is like your fingers are a train, going down a pair of railroad tracks.
Teach your toddler the railroad sign when you see it in stories or pictures, or better yet, when you are on a scenic train ride during a holiday.
This is a useful flash card taught best in conjunction with other land travel and nature flash cards. Teach the signs in advance, then have fun using the signs to describe the scenic view you can see from your train car window!