grayscale tablet drawings or M1 style, it is used in the Yukkuri Hardship series (including Orphan Alice) and several one shots.
grayscale and B/W mouse drawings or Mouse1 style, it is used in wall-of-text stories and some comics and illustrations, grayscale drawings can be easily confused with M1 style.
B/W sketches made with tablet or S1 style, it is used in most recent illustrations and comics.
A couple of notable exceptions are the first editions of Yukkuri Hardship #1 and #2, these were pencil and ink drawings.