A copyright symbol is used to indicate that somebody legally owns the rights to make and distribute copies of a particular work. Generally, you'll see a circle "C" copyright symbol on works such as TV ...
Following Marvel Studios' decision to basically spoil the ending of Thunderbolts* by revealing that the asterisk in the title actually refers to The New Avengers, the official Avengers social media ...
The copyright symbol originated in the US copyright law, according to which a work was required to have a proper copyright notice. Without this notice, the work would not be protected by copyright.