Registering US copyrights hasn't been necessary since 1978.
Under US law, for unregistered works, you can only sue for actual damages and the infringer's profits attributable to the intfringement, which for an I-D would be pretty hard to show.
Once they're registered, you can sue for statutory damages which can be substantial. See 17 USC 504.
Regards, John Levine, johnl@xxxxxxxxx, Junior Lawyer 2nd class Please consider the environment before reading this e-mail.