This a Keep It Simple Label to indicate that you reside in a US state (e.g. Alabama. It automatically adds users who display it to (for example) the Users in Alabama category.
Usage edit
{{WP:KIS/US state|AL}} links to Wikipedia:WikiProject Alabama.
{{WP:KIS/US state|AL|article=yes}} links to Alabama state's article.
Replace "AL" with your state's postal code.