What is the possessive form of "U.S."? Is it U.S.' or U.S.'s?
The possessive from of "U.S." is U.S.'
Possessives of abbreviations are formed exactly the same way they would be if the noun was spelled out completely.
The single possessive is formed by adding an -'s to the end of the noun.
The plural possessive is formed by just adding an apostrophe to the end of the noun.
This is where it gets a little tricky. The "United States" is a singular noun, we always say that: "The United States (U.S.) is. . ." not "The United States (U.S.) are. . ."
The United States is actually a noun in plural form (it ends in an "s") but is singular in meaning. The possessive form of these nouns are always the same as plural nouns so, for example:
United States' (U.S.')
I hope this helped!