The Method Signatures dialog was introducted in Signatures button. You can display this dialog by clicking Signatures... in the Generic Function Browser.
By default, the Method Signatures dialog displays the signatures of all methods defined on the generic function. When there are many methods, or when the distinction between different classes is not clear, this can be confusing.
To simplify the display, you can restrict the signatures displayed to a chosen class and its superclasses. To do this, enter the name of the chosen class into the Restricted Class panel. As with similar text boxes in Common LispWorks, click 
to confirm your choice, 
to cancel the current setting, and 
to display a list of possible completions.
Figure 13.4 Restricting the signatures by class
Once you have made a choice, only those signatures that contain the specified class or one of its superclasses are listed in the Signatures panel of the dialog. This simplified display is useful when there are a large number of complicated signatures.
Be aware of the difference between this approach and the use of the Argument box in the Signatures panel. Restricting signatures confines the signatures offered in the dialog by means of the class of the signatures.
Click 
to display the signatures for all methods defined once again.