@Iggy
In the United States, anything you create is automatically copyrighted, and that copyright extends to all signatories of the Berne Convention. This is why it's humorous whenever someone says something like "downloading copyrighted works is illegal." Unless explicitly placed in the public domain, everything is copyrighted. If you couldn't download copyrighted works, you couldn't receive Ethernet frame headers, which could arguably be copyrighted by the entity that produced them.
Forums like this one may have terms of service that alter ownership or create specific license terms for copyrighted content, but typically, yes, anything you write is copyrighted.