There are two reasons for underscored text, one old and one newer.

The old underscore was used for typewriters that could not print text that was in italics or bold face and so the underscore was used to indicate text that would be stylized. The underscore is not used in contemporary typesetting because italics and boldface exist as an option.

The newer use of underscore is on the web to indicate text that is hyperlinked.

Any other use of the underscore is simply not acceptable

Gary