A more thorough explanation:

A comparison signal, also known as a compare with signal, is a signal used in legal writing to encourage the reader to compare at least two cited sources. The purpose of comparing the sources is to either support or clarify the author's preceding statements.

Here is an example of how to use a comparison signal:

Compare [source 1] with [source 2].

Or, with more sources on each side of the comparison:

Compare [source 1] and [source 2] with [source 3] and [source 4].

For instance, in a legal brief or decision statement, one might write:

"Circuits were split on the issue of whether the SCOTUS decision of Crawford v. Washington applies retroactively to previous convictions or not. Compare Bockting v. Bayer, 399 F.3d 1010 (9th Cir. 2005) with Mungo v. Duncan, 393 F.3d 327 (2d Cir. 2004)."

In this example, the comparison signal is used to show that different circuits disagreed over the issue of retroactively applying the decision of Crawford.