Meaning of Objective-C macros prefixed with an at (@) symbol

The ReactiveCocoa framework makes use of weakify and strongify macros, both of which are preceded by an '@' symbol.

Here's an example (From this file).

- (RACSignal *)rac_textSignal {
        @weakify(self);
        return [[[[RACSignal
                ... 
               ];
}

What is the significance of the at symbol that is a prefix to the macro name? (NOTE: I have checked the macro, and it is called 'weakify', not '@weakify', so it isn't just the macro name!).

The macro itself is defined here:

https://github.com/jspahrsummers/libextobjc/blob/master/extobjc/EXTScope.h#L45