Thinking about it, there's a few things that help make some countries loco's distinctive (or in the case of the UK, the complete lack of any of them!). I can't think of a German engine that doesn't have those very distinctive plates at the front (they're Smoke Deflectors, intended to lift smoke away from the front of the engine & improve visibility for the driver). UK engines did also use them, but they weren't as standardised, prominent, or universal (plenty of classes never had them).

On US loco's there are a few things, and again, these are just things that have stuck in my mind - I'm no sort of expert on US steam. One is that every engine I can think of has a very large & prominent central headlight, much more obvious than on European models. Another, is the pilot (cow-catcher), rarely seen on UK trains. A lot of US engines also seem to have quite distinctive cabs - longer than European cabs & with the roof extended slightly backwards. Finally, on earlier US engines there is, of course, the very distinctive coffee pot stack. This is actually a spark arrestor, apparently, as many early US loco's burnt wood rather than coal. This meant they produced & ejected far more embers, with a consequent higher risk of trackside fires. As more & more engines were designed for coal, those chimneys disappeared.

I think you're probably also right about the cleaner lines of UK engines, Joe; German ones seem to carry a bit more, though not, perhaps, as much as US. As for that gubbins at the front of 556, I can't find anything definitive, but I'd guess, this being an Alaskan engine, that it's some kind of heating device for the snowplough / front of the train. There certainly seems to be some pipe-work going forward & down behind the plough.