When aluminum (or any other substance) is embossed it is squished between two dies, a male and a female, so that the characters, be they letters or numbers end up being raised toward the reader of the tag. The embossed tag looks clean and sharp, with each character having a uniform look.
When aluminum is stamped, the characters are merely mashed or cut into the aluminum with a male die only. The stamped tag is somewhat harder to read, and the characters are not as uniform.
Learn more about Premax embossed aluminum tags.