Supposedly, the ears are farther back on the head and somewhat lower. Gauge it by the distance from eye to ear.
Also the brow and nose are flatter, or even convex.
The eye (and this is subjective) is like looking at a wet black stone, impassive and uncommunicative.
An Angus eye is full of ambiguous animation, and a shorthorn eye is thoughtful or skeptical, but a Galloway eye is dark as a cave.
This is impossible to quantify, I realize, and probably more of an intuition than anything. Perhaps an inappropriate topic.
https://books.google.com/books?id=I-06Yneo-UIC&dq=Galloway%20ear%20set&pg=RA3-PA13#v=onepage&q=Galloway%20ear%20set&f=false
Galloway.—Head short, wide, with broad forehead and wide nostrils; poll flat, with no evidence of horns or scurs; ears with long hair.and set rather further back than most breeds, pointing upward and forward
In form the Galloway is low-set and deep, but proportionately longer than the Aberdeen Angus and flatter of rib. The head is somewhat similar to that of the Angus except that the poll is not so sharp. The head is covered with long, wavy hair, and the ear is set farther back from the forehead. The body is long and of medium depth.