Citation, Documentation of Sources
Q. How does Chicago treat Twitter handles? Do you lowercase (or capitalize) them consistently, or do you follow the user’s preference? For example, how would you style the following handles in a story: @roseannecash, @ElizabethHurley, @leannrimes.
A. CMOS is silent on the issue, but it’s probably best to cap them the way they appear at the Twitter site, since that’s the way the owners styled them.