During the day, no lights are required (but you can use lights as you would during the night). At night, signal Fz1 must be displayed, which is one white marker light near the buffers. Using all three lights as you would on a mainline move (Signal Zg1a) is also permitted though, and this is what everyone actually does these days. In fact, if during shunting you pass over a level crossing that doesn't have active protection, using all three lights is mandatory day and night. You don't need end of train markers or anything for shunting, so you can just have Zg1a or Fz1 on on both ends and save yourself the faff of changing the lights whenever you switch direction.
This seems to have become the norm, as far as what I've seen in freight yards lately. Especially on locos with older-style lightbulbs like the 363 and 294, I could imagine it also slightly extends the lifespan of the bulbs.
That makes sense, since the worst stress on filament bulbs is when you turn them on. Personally, I usually do Zg1a on both ends when I'm shunting with a big mainline loco, but in the 363 Fz1 on both ends just feels better somehow.
I was told by a BR294 driver, though I might be misremembering (because I was more focused on the physics data ) that Fz1 meant that you would turn on the headlight (and taillight iirc) closest to the station building, or if there is no station it would be the right in the direction of travel. So for example if you are shunting at Mainz-Bischofsheim and facing north you would have the right headlight/taillight turned on.
