I have two problems with the phrasing here:

> Called **every time** a new subscriber subscribes to the signal.

Mentioning "new" makes it sound like it won't be called twice if the same subscriber subscribes to twice. Doesn't it though?

> The new <RACSubscriber>, which represents the created subscription, is passed in.

"The" implies the subscriber that subscribed to the signal is passed in, even though "which represents the created subscription" says otherwise.

It all makes perfect sense if you know how it's implemented, but it's very confusing otherwise.

My suggestion:

```objc
/// didSubscribe - Each time the created signal is subscribed to, a new
///                <RACSubscriber> object is created for that subscription and
///                passed to this block.
```