Not necessarily. If you want to avoid situations where title points at a mutable subclass, yes, but if that isn't a concern, there's nothing inherently incorrect with a simple retain.
"copy"ing an immutable string just retains it, so there's little benefit to using a retain property for NSString properties, or for properties of the other NSMutableCopying type families. As a best practice you should always use copy properties for them.
Except that if someone modifies the string they passed you, your 'copy' of the string will also change.
That would only occur if it was an NSMutableString, like the GP said.