I have a question about the appropriate use of an apostrophe. How do you make the abbreviation US for United States possessive? Is it US's or US'?
The rules are a little weak on this. Both are acceptable, depending on whose book you're using.
A good rule of thumb is that if you pronounce the second s, show it: US's. If you don't, don't: US'.
I pronounce the second s, so I write it US's. (Actually, I write it U.S.'s.)
Let's see what others have to say....