Assignment of copyright

Recently, Mary Brandt Jensen wrote, regarding assignment of copyright:

"The author of the paper retains the copyright unless he specifically dedicates the work to the public domain or assigns the copyright to someone else. ...
...the law requires assignments to be in writing and signed by the author."

(Extract is from "sandboxes and copyright" thread)

Does anyone have any info on a recent ruling for Nagel estate v. Playboy Inc. that held a check (signed by Nagel, on which Playboy had placed a statement concerning assignment of rights to his illustrations) was insufficient to assign copyright to Playboy?

What are the precise requirements for assigning copyright? Was there an 'intent' argument made?

Dr. Paul E. Filmer                      | (202) 479-2609 voice
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