In light of the U.S. Supreme Court hearings on same-sex marriage, millions of Facebook users have changed their profile images in support of same-sex marriage.

Earlier this week, The Human Rights Campaign, a group which lobbies for lesbian and gay rights, encouraged Internet users to change their Facebook profile pictures to a pink-and-red version of the HRC's equality logo.

Facebook researchers found that the campaign was effective, detecting a measurable lift in profile-picture activity.

"Since then, we've noticed a surge in people changing their profile photos to various versions of this image," Facebook researcher Eytan Bakshy writes on the Facebook blog.

According to Facebook's internal data, more than double the usual number of users—2.7 million—updated their profile photos on Tuesday, as compared to the week before.

Bakshy notes that the 120% increase in photo updates started right around the same time the HRC began urging people to make the change (indicated by dashed line in the chart below).

Here are some other stats:

Across all age groups, more Facebook users changed their profile photos as compared to the week before.

Facebook users closest to 30 years old made the most profile photo changes. About 3.5 percent of 30-year-old Facebook users changed their profile image in support of same-sex marriage.

The county with the most profile-change activity was estimated to be Washtenaw County, Michigan—the location of the University of Michigan. An estimated 6.2 percent of Facebook users from this county changed their profile photo in support of the campaign.