When denoting ownership and a word ends in the letter "S," an apostrophe is placed after the "S"; for example, "The North Stars' first championship game." An additional "S" can also be written, and the apostrophe can be placed between the two; for example, "Put that in the Jones's mailbox." Both methods are linguistically correct; however, consistency is necessary for clarity.
Apostrophes signal ownership. Frequently newspapers and magazines make a distinction between proper nouns and common nouns that end in an "S" by placing an additional "S" at the end of common nouns. They allow proper nouns to use an apostrophe alone; for example, "the bass's speaker" versus
"Kansas' town square." They are never used to turn a singular noun into a plural noun unless that noun is an abbreviation. In this case, occasionally an apostrophe is used to create a distinction between the final period in the abbreviation and the ownership "S"; for example, "There are three M.D.'s in the practice."
When a noun is used as an adjective to describe a second noun, no apostrophe is needed. For example, the following is correct: "I'm a United States citizen." In comparison, the following is incorrect: "I'm a United States' citizen."