Facebook became a sea of red on Tuesday with many users posting a photo of a red equal sign in solidarity of the Supreme Court gay marriage hearings.

But many confused by the symbol have taken to the web to learn what the red equal sign means, like on AskMeFast.com, where a user asked, “What is this red square with pink equal sign being used as profile pic on fb?”

To answer the question: Many marriage equality activists have camped outside for days ahead of Tuesday’s Supreme Court hearing regarding Prop 8, and those who could not be on site in Washington D.C. have taken to Facebook by posting a photo of a red equal sign.

The photo originated from the Human Rights Campaign’s red equal sign to signify their support as the hearings begin. In fact, Human Rights Campaign is urging all Facebook users who support gay marriage to change their profile pictures and avatars to the red equal sign photo.

"Follow @HRC on Twitter and at www.hrc.org/blog for live-updates from the first day of at the Supreme Court hearings. Make sure you wear red to show your support for marriage equality. And make your Facebook profile red too!," the post says.

Usually blue a blue box with an equal symbol, the updated logo in a bright hue of red is in observance of the SCOTUS hearings, where the United States Supreme Court will begin to hear two gay marriage cases to determine the constitutionality of California’s Proposition 8 and the Defense of Marriage Act, or DOMA. Prop 8, a California law that ruled only marriages between a man and a woman will be recognized by the state, was ruled unconstitutional by the Ninth Circuit Court of Appeals. The constitutionality of the ban on same-sex marriages will be heard by the Supreme Court as part of the Hollingsworth v. Perry case.

The red equal sign has also extended to celebrities’ Facebook pages, with gay rights activist and “Star Trek” actor George Takei leading the pack. By Tuesday afternoon, Takei received nearly four million likes and nearly 30,000 shares for changing his photo to a red equal sign.

“For those friends wondering, this special ‘red’ equality symbol signifies that marriage equality really is all about love. Thanks to the Human Rights Campaign for this effort. Please consider changing your profile today in support--esp if you are a straight ally,” he wrote.

Also, check out some of the funniest red equal sign memes that have spawned from the rampant sharing on social media.