I have seen some steamers in videos with the bell ringing incessantly while on the move, no matter where or what speed.
I know that bells are often rung at crossings with roads. Bells are rung on approach to a loading platform to alert ground personnel and people waiting to board to be alert. Bells are rung just prior to the engine moving, but the whistle is also sounded before any move from stationary.
Bells are also rung in yards while the engine is in motion.
But, in the end, it depends on federal rules and/or their interface with the company rules.
-Crandell