A well-known crank, let's call him "Wolfgang", uses ten different sock-puppets to dump his pseudo-scientific nonsense into several Stack Exchange sites. Every time another user, let's call him "Uwe", notices Wolfgang's questions or answers, he adds a comment "Warning: "Forte" is one of Wolfgang's ten sock-puppets, and discussing with Wolfgang is known to be pointless". Then Wolfgang changes the display name of his sock-puppet "Forte" to "Uwe", which not only confuses other readers, but makes commenting quite difficult for Uwe. Is this considered as acceptable behaviour, or is it something that moderators (have to?) deal with?
In general, these sorts of confrontational asides are not useful on SE, as they leave moderation up to underinformed public opinion and a he-said/she-said muddle. (On the plus side, the popcorn industry gets a boost.)
Don't post these passive-aggressive comments, especially not preemptively. Instead, flag for a ♦ mod if someone is using sock puppets to evade account restrictions on posting (including suspensions), or to create confusion with other users' names. Disruptive usernames will likely be changed by ♦ mods, per What are the rules governing display names and avatars?
Also flag for a ♦ mod if an account is routinely posting low-quality posts that do not trigger the automatic bans. There is a suspension reason for this. If you don't have enough room in the flag reason box, use either a deleted answer of your own to contain the overflow (linking to it from the flag) or use the Contact form. Make sure you have at least some evidence that does not depend on the mods being subject-matter experts in the particular tags involved. (Although, of course, expecting e.g. Physics SE mods to know something about physics in general is perfectly reasonable.)