They're popping up on Facebook news feeds around the nation, but without much explanation. Just what are those red equal-sign Facebook profile pictures all about? Look no further than the Human Rights Campaign, an organization in support of gay marriage that is running a particularly successful social media initiative as the Supreme Court discusses the issue over the next two days.

Social Trend: Facebook profile pictures changed to HRC's equal sign as SCOTUS argues gay marriage.

In a Facebook post today, the HRC asked gay marriage supporters to " paint the town red," wearing red in their wardrobe as well on their Facebook pages, changing profile photos over to the HRC "=" logo. The idea has even caught the eyes of Congress, with 13 members showcasing the symbol, according to Ryan Beckwith.

Updated: 13 members of Congress changed their Twitter avatars in support of gay marriage today. bit.ly/YCp7sI #SCOTUS #Prop8

— Ryan Teague Beckwith (@ryanbeckwith) March 26, 2013

The campaign has left many on Twitter wondering what changing a profile picture will accomplish.

Just got off the phone with #scotus justice Scalia. Said he was going to vote no until he saw all the red profile pictures on FB. #pointless

— Eric Arnold (@DudeImEric) March 26, 2013

Boston comedian Dana Jay Bein had a more optimistic outlook in a Facebook post: "Seeing all of the people who support can inspire people to take MORE action - small change. I'd much rather see red equal signs than pictures of Grumpy Cat and ironic self shots."

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The HRC initiative has seen a few spin-offs since this morning, with several profile picture explanation posts seeing high numbers of shares, in an attempt to clarify what the red profile pictures stand for.