Proper Apostrophe Usage with Initialisms: CCS' or CCS's?

Solution 1:

According to the Guardian style guide:

The possessive in words and names ending in S normally takes an apostrophe followed by a second S (Jones's, James's), but be guided by pronunciation and use the plural apostrophe where it helps: Mephistopheles', Waters', Hedges' rather than Mephistopheles's, Waters's, Hedges's.

So I would likewise go by pronunciation write it as:

Buy CCS's New Product.

Or rewrite to avoid it the apostrophe altogether.

Solution 2:

Seems that lawprose agrees with CCS's.

"Acronyms and initialisms. It doesn’t come up often (and it’s easily avoided), but the plural possessive of acronyms and initialisms follows the general rule. Take the singular {an MRI}, make it plural {two MRIs}, and add an apostrophe {the three MRIs’ role in the diagnosis}. If there’s a plural word in an initialism — as when Lloyd’s Register Drilling Integrity Services becomes the singular name LRDIS – treat the full initialism as a singular and make the possessive form singular {LRDIS’s contentions}."

From http://www.lawprose.org/blog/?p=1357