Here’s a picture of the modem cord from an IBM laptop.
A “Do Not Open” warning is on the plastic bag containing the modem cord. I guess IBM does not want me to use this cord!
An explanation may be that the “Please do not open” and “ferrite cord case” on separate lines may be meant to be one complete sentence “Please do not open ferrite core case.” But this leads to more questions – why make part of the “sentence” a larger type face? Or better yet – why not put the warning directly on the ferrite case instead of the throwaway plastic bag?