For most of US history, copyright was something you had to ask for. To copyright a work, you'd send a copy to the Library of Congress and they'd issue you a copyright. Not only did that let you display a copyright mark on your work - so people would know they weren't allowed to copy it without your permission - but if anyone wanted to figure out who to ask in order to *get* permission to copy or adapt a work, they could just go look up the paperwork at the LoC.
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