The US may as well be renamed the land of the red, white, and pink on Saturday, January 21.

An estimated 500,000 people gathered for the Women's March on Washington to advocate for gender equality on President Donald Trump's first full day in office. Many sported pink knitted beanies with cat ears, called "pussy hats," as a symbol of solidarity among protestors.

A group called the Pussyhat Project helped make the hat part of marchers' uniform. Project co-organizer Jayna Zweiman told Business Insider that anyone who planned to march could download a crochet, knit, or sew pattern for the hat on the project's site. Alternatively, people could make and send them to the organizers to give away at DC's march.

Paige Carmichael, 6, from Chadds Ford, Pennsylvania, participates in the Women's March on Washington, while wearing a pink beanie and a homemade shirt that reads, "The future is nasty!" Lucy Nicholson/Reuters

Since it launched in late November, the project has garnered thousands of social media followers, and Zweiman estimates nearly 100,000 people have downloaded the hat's pattern. Amy Schumer, Patti Smith, Rosanne Cash, and Krysten Ritter have posted photos of themselves wearing the hats, too.

Actress Jessica Chastain ("The Martian," "Zero Dark Thirty") handed out buttons at the Women's March on Washington while wearing a pussy hat.

Jessica Chastain attends the Women's March on Washington on January 21, 2017 in Washington, DC. Theo Wargo/Getty

Following the election, Zweiman and co-organizer Krista Suh designed the hat's pattern with the owner of The Little Knittery, a Los Angeles-based knitting shop. Besides the cat-ear shape, the hat's name was inspired by Trump's 2005 comments in the Access Hollywood audio leaked in October 2016, in which he bragged about grabbing women by their genitals.

The Pussyhat project is "about women refusing to be erased from political discussion," Suh said.

The team has also organized knit-alongs — where people can learn how to make the hats together — in 100 knitting shops across the country. Suh and Zweiman said they have received hats from people outside the US, including those in Scandinavia, New Zealand, and Canada, who could not make the march but wanted to show support.

Jayna Zweiman and Krista Suh take part in the Pussyhat social media campaign they created to provide pink hats for protesters in the Women's March on Washington. Lucy Nicholson/Reuters

Suh said she received an email from a daughter whose mother participated in the 1963 March on Washington with Dr. Martin Luther King Jr. For this march, however, the daughter needed to take care of her mother, but they knitted and sent their hats to the project's organizers "to represent their family at the march."

Two days after the project's launch, Zweiman also received a note from a woman whose daughter used to be an avid knitter. But she quit after she suffered a brain injury and had trouble maneuvering one of her hands. The pussy hat, which is a simple pattern, inspired her to start looming again.

"No matter who you are, no matter what your skill-set is, people can help you make it. Everyone can participate," Zweiman said.