Cocos2D displays the frame rate i.e. the number of frames per second in the bottom left corner of screen when the scene is rendered. This is a very useful piece of information for debugging purposes
because it allows you to see the frame rate your game realtime as it runs. The higher the frame rate the better is your game display performance. The max value of the frame rate is 60.

In order to disable the frame rate display.

set the following to NO in your App Delegate class e.g.  in AppDelegate.m

[director setDisplayFPS:NO];

in order to enable it set it to YES as

[director setDisplayFPS:YES];