Old habits die hard. When I suggest that lawyers italicize case names, they often react in horror. But the modern preference is to italicize case names, rather than underscore, although either is correct. I know. You still don’t believe me. Since my word on this issue may not be enough to slant you (pun intended!) in the proper direction, here’s the reason why.
In the old days (before computers), lawyers underscored case names and introductory signals because typewriters and early word-processing programs could not italicize. So briefs that were professionally printed used italics, but briefs that were typed in-house had to make do with underscoring. Although most style manuals say that case names may be italicized or underscored, it makes sense to drop the obsolete convention of underscoring now that typewriters are being turned into jewelry.
All the authorities agree on this. The style guides still allow underscoring out of deference to anyone who may still be typing on an old typewriter. Contrary to popular perception, The Bluebook does not require underscoring. It gives the option of either underscoring or italicizing (see bluepages at front, B13 on typeface conventions), but it then confuses the issue by using underscoring throughout. (Did you expect anything but confusion from The Bluebook?)
The ultimate guru on all things related to the design of legal documents is Matthew Butterick. (His book, Typography for Lawyers, is groundbreaking. You should buy it.) He insists on italics for case names and also explains that the Bluebook does not require underscoring. Bryan Garner also endorses italics. And Supreme Court briefs use italics. Here’s an example: Supreme Court Brief using italics.
Italics follow the design principle of keeping the fonts on a page as simple and consistent as possible. Italics are just easier on the eye.
So tilt away!
P.S. My book contains many other fascinating tips like this.