Allison, who didn't want to reveal her last name, told BuzzFeed News on Wednesday why she started the #SafetyPin campaign: "I thought about something that would cost nothing and had no political affiliation. Something that says, ‘I am a safe space, you can sit next to me, you can talk to me, you can ask me for a help'."
Many people got involved and tweeted selfies of themselves wearing a safety pin.
However, the campaign has been criticised on Twitter, particularly by people of colour who have personal experiences of racism.
Some complained the safety pin wasn't a helpful tool to combat racism at all, but rather a way of making people feel better about themselves.
Some have noticed it was predominately white people who participated in the hashtag.
Jason Okundaye, 19, a student at Pembroke College, Cambridge, told BuzzFeed News he was frustrated by the sudden acknowledgement of racism from peers "who usually turn a blind eye".
"What prompted me to tweet about it was my surprise at seeing peers who usually turn a blind eye to racism in everyday situations suddenly becoming the saviours of all immigrants and people of colour," Okundaye said.
He added: "I'm sure people mean well but there is a very transparent 'white knight' narrative which underpins the campaign as many seem to have used this 'safety pin solidarity' as a way to capitalise off the escalating racism and xenophobia post-Brexit.
"I'm frustrated that when people of colour spoke about our lived experiences of racism before, we were dismissed and told to stop exaggerating. I'm frustrated that people won't challenge, for example, the fact that racism is the infrastructure on which Western society was built, or consider the damaging racial bias prevalent in things like presentation of beauty or media representation."