How does one typically illustrate local var assign

[dsargrad]

How does one typically model the assignment of a key local variable within a sequence diagram?

[«Midnight»]

Self message? Note (perhaps attached to the method call that makes the assignment)?

Most of the time this would seem internal to a method, it would be below the level of the diagram. Something that stands out from the 'usual' notation should serve to call attention to the change, without indicating an additional operation of the class.