I heard that there was an in joke in the credits of Robocop. Is that true?
Yes, in the closing credits:
The final paragraph states:
THIS MOTION PICTURE IS PROTECTED UNDER THE LAWS OF THE UNITED STATES AND OTHER COUNTRIES AND ITS UNAUTHORIZED DUPLICATION, DISTRIBUTION OR EXHIBITION MAY RESULT IN CIVIL LIABILITY AND CRIMINAL PROSECUTION BY ENFORCEMENT DROIDS
"Enforcement droids" is clear reference to the ED-209.