If you've been on Facebook at all today, you've probably noticed that several of your friends have changed their profile pictures to a red box with a pink equal sign inside of it.

But what does it mean?

The symbol, also known as the "Red Equals Sign" is a viral campaign of support for marriage equality launched by the Human Rights Campaign, an organization that describes itself as working towards an "America where lesbian, gay, bisexual, and transgender people are ensured equality at home, at work, and in every community."

The nonprofit first posted the image on its Facebook page on Monday in the wake of the Supreme Court hearing arguments over two significant cases—the constitutionality of California's Proposition 8 and of the Defense of Marriage Act (DOMA)—that could decide the fate of same-sex marriage.

"Who's wearing red tomorrow?" asked the HRC.

That single post was shared more than 51,670 times and liked by 15,691 people.

Earlier today, the organization doubled their efforts and posted the image again. That repost went viral, with 32,452 shares and 11,259 likes.

Also throwing his support behind the HRC initiative was advocate/actor/Facebook celebrity George Takei, who encouraged his fans to use the red equals sign as a profile picture.

"Tomorrow, the U.S. Supreme Court hears argument on two critical marriage equality cases," noted Takei yesterday. "I'm changing my profile pic for the next two days to help bring attention to this important and historic occasion."

"Friends, you can all say you know at least a gay couple who are married— George and Brad Takei. I hope you value our marriage as equal to any other between two loving adults. Thank you."

Takei's post garnered 11,944 shares and 144,071 likes.

Photo via Human Rights Campaign/ Facebook