Ms Spencer's original tweet has been retweeted 16,000 times, attracted 14,000 comments and 102,000 likes. Her friends have now joined in.
"Every day I carry my gun and/or knife to ensure I never have to say #MeToo," tweeted Brittany Self, along with a similar photo revealing a handgun tucked into her pants. "Instead, I say #NotMe in solidarity with my best friend @BrennaSpencer #2A"
According to her LinkedIn page, Ms Self is a fellow Tennessee communications graduate and works as a marketing co-ordinator at Japanese healthcare firm Kobayashi Pharmaceutical.
Antonia Okafor, co-founder of EmPOWERed, a lobby group advocating for the rights of female college students to carry guns on campus, tweeted a similar photo. "In solidarity with emPOWERed woman, @BrennaSpencer," she wrote.
In the US, only five out of 50 states ban the open carrying of handguns, while every state allows the carrying of concealed weapons in some form, although typically a permit is required.
Fellow Turning Point USA employee Alana Mastrangelo also joined in. "ABC News called the police on my friend, Brenna Spencer (probably hoping to get a better story)," she wrote.
"Here I am in solidarity with Brenna, also carrying in public. We will NOT allow for leftist intimidation tactics to hinder our inalienable #2A rights."
On Wednesday, Ms Spencer told Fox News it was "really, really important to empower the tens of millions of gun-owning women and let them know that they have a voice".
"Sexual assault has grabbed a lot of attention these past few years ... so I think it's important for women to be able to know they are their first line of defence," she said.
"The Second Amendment has been under attack, especially on college campuses, so not only do they try to restrict our right to carry on campus, but they also are trying to up the age to 21 to buy a gun. It's really, really important to stand up for what you believe in. It's important to voice your opinions."
Last month, more than 200,000 protesters descended on Washington DC to call for stricter gun control in the wake of the Parkland massacre, which saw 19-year-old ex-student Nikolas Cruz shoot dead 17 children and staff members.
Survivors including 18-year-olds Emma Gonzalez and David Hogg have been embraced by left-wing media as new anti-gun spokespeople, while fellow Parkland student Kyle Kashuv has similarly been embraced by right-wing media due to his pro-gun stance.
According to the Gun Violence Archive, there have been 62 mass shootings, 3889 gun deaths and 6797 gun injuries in the US in 2018.
