= Queen's Counsel.
A. Plural Form.
Though some writers make the plural form Q.C.s, the better form is Q.C.'s.
B. Punctuation with.
When the title appears in midsentence, a comma goes before and after it:
“Roman law texts were also cited by Sir Sidney Kentridge, Q.C., counsel for the claimants.”
Basil Markesinis & JÖrg Fedtke, The Judge as a Comparatist, 80 Tul. L. Rev. 11, 96 n.279 (2005).
Some writers omit the periods in this abbreviation—e.g.:
“If a client wants to employ a Queen's Counsel or senior barrister, he must also employ—at two-thirds the QC's fee—a junior barrister as well.”
Anthony Sampson, Anatomy of Britain 149 (1962). The prevailing style—in BrE and AmE alike—is to include the periods.
Garner’s Dictionary of Legal Usage, Bryan A. Garner