A symbol next to them mean they have been banned for cheating.
Account Closed Symbol

When member close their own account, their contents may remain here to be seen.
[Although a member may ask for their content to be hidden when they close it. Mod.]

As an addendum, titled players closed for cheating don't get the 'cheater' icon (this is a chess.com general policy).

Yes...And an account closed with no symbol means the player closed his own account?
It can also mean the account was closed by chess.com, but not for cheating (spamming, sandbagging, multiple accounts...)
I've noticed that some players who have closed accounts have the little symbol next to their name, and some do not. Is there a way to differentiate between a player closing thier account and chess.com doing so?