All Bavarian locos had bells and whistles. Wrt usage, the bell was rung when approaching ungated crossings and continuously rung until the loco had crossed. The whistle was used as well if there was poor visibility (tunnels, curves or bad weather) or lots of noise e.g. when crossing a road when motor vehicle sounds might drown out the bell.

It was not generally left to the driver, bell and whistle boards were clearly placed.

Whistles were also used as signals e.g. at stations on branch lines to announce the arrival of a train.

I imagine the DRG was similar.

Paul, of (formerly Prussian-occupied) Lower Saxony