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Legally speaking, you don't file "for" a copyright, as one exists already under U.S. law. But you can register your copyright, which is advisable., because you are protecting the rights that you do have and would be able to sue for damages, attorney fees and costs, etc... if there was an infringement of those rights.
It's actually not even necessary to put the circle c designation on your work tocopyright it. Rather, the circle C is merely an indication that you're claiming copyright status inthe work, not that it's actually copyrighted. Under US law, a copyrightable work is automatically copyrighted. So even though it is not registered with the US copyright office, once it is created it is under copyright protection. If you can show that you created it before they had the "idea" then you could have some legal recourse
A copyright registration costs about $35 if you do it online. You do not even need an attorney to register online, you can go to Copyright Registration and complete the online registration and send a pdf or other type of file with the copyrighted works attached and you would be protected.
Hope that clears things up a bit. If you have any other questions, please let me know. If not, and you have not yet, please rate my answer AND press the "submit" button, if applicable.
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