Which preposition to use with underscores

with Occurrences 2%

The defendant, while professing to be a total abstainera man who, in my own knowledge, has refused spirituous refreshment as an inordinate weakness of the flesh, with shameless hypocrisy underscores with his pencil the following passage and presents it to the plaintiff.

at Occurrences 1%

However, it was read in due time; for, finding himself in a lonely place that afternoon, Tom pulled it out with an anxious face, and read a letter written in a hasty ill-formed hand, underscored at every fifth word, and plentifully bedecked with notes of exclamation.

for Occurrences 1%

And it is just this: a superb story, with underscoring for "story.

Which preposition to use with  underscores