If you’ve logged on to Facebook or any other type of social media today, you may have noticed that the Internet is awash in a sea of red and pink. Many people have changed their profile pictures to be the same image: two pink bars on a field of red. What is it?

That’s the “Red Equals Sign” and it’s a symbol for marriage equality. Today is the first day of Supreme Court oral arguments over the constitutionality of California ballot initiative Proposition 8. Passed during the 2008 elections, Prop 8 defines recognized marriage in California as only valid between a man and a woman.

The Red Equals Sign has been championed by the Human Rights Campaign, an activist group that works for lesbian, gay, bisexual and transgender equal rights. The campaign urges people to wear red today and has organized for people to stand outside of the U.S. Supreme Court while the ballot initiative is being debated inside. 

The group has galvanized social media with the Red Equals Sign as well as the hashtag #UnitedforMarriage.

Over the past couple of years, the Internet has occasionally flared into a hotbed of activism around particular issues, especially pertaining to court cases and proposed legislation. The most famous instance in the past year was when the Web “blacked out” as a response to the Stop Online Piracy Act (SOPA) in January 2012.

Among other things, SOPA would have allowed the federal government to effectively “black out” sites accused of fomenting copyright infringement without judicial involvement or much in the way of due process. Sites such as Reddit went completely dark that day and even search behemoth Google blacked out its logo as part of the activism against SOPA. 

Did you change your Facebook profile picture today to support marriage equality? Let us know in the comments.