Since Objective C doesn't support namespaces, it is good to use prefixes for category methods like this:

@interface UIViewController (MOUIViewControllerAdditions)

- (void)moSomeFunction1();
- (void)moSomeFunction2();

@end

Notice that the category name has the same prefix (“mo”). It is especially important to give a prefix to your category methods because good function names can easily clash with an existing method of the same class either in the existing SDK or in a future version and be hard to detect.

It's a good habit to do the same thing for class names if you want to package them into libraries:

@interface MOMyClass : NSObject

@end

Use any prefix — one that is an abbreviation of your name or your company's name is good — as long as it isn't used by Apple or in popular open source libraries, e.g. stay away from the NS and UI prefixes as they are used by Apple.