It might not have the instant recognition of 10 Downing Street or 1600 Pennsylvania Avenue.
But in the past eight years more than half a million people have sent mail to 13345 Copper Ridge Road, Germantown, Maryland 20874.
Each has been an anonymous postcard, containing a secret the writer has never told anyone before.
And Frank Warren, who began the project in 2004 from his home address, has read every single one.
“I have this photographic memory of them where the secrets stay with me,” says Warren from his Maryland home. “I carry them closely – they are very important to me.”
Every Sunday Warren posts a minimum of ten postcards on his blog, which has now received upward of 573 million views. He has also released collections of the postcards in book form, proceeds of which support the ongoing project, as Warren has refused to put any adverts on his blog.
“I see something every 20 minutes which reminds me of somebody’s secret,” he says.
“They are part of my life. Not long ago I was getting into an elevator and I just remembered this postcard where someone said: ‘Whenever somebody pushes a button for a floor higher than mine I feel inferior to them’.”
Postcards have included proposals of marriage, confessions, random acts of kindness and cheeky practical jokes.
“One of the ways I have changed through the project is I have become more accepting of not just other people’s behaviour, but my own,” he says.
“I understand human nature in a much broader way. You can step out of stereotypes and expectations – you can see through the secrets that all of us live outside of the box society would put us in.
“There was the cashier who around Christmas time without anybody noticing gives discounts to people who look like they need them, or the person who drops a dollar bill on the sidewalk so others might feel lucky.
“One that will stay with me for a long time was about someone who, when they mail a bill they don’t want to pay, sticks the cheque between their buttcheeks before they put it in the envelope.
“Sometimes I will pull secrets out of the mailbox that come from different continents but express the same yearning, hopes or sexual taboos. You would think that secrets divide us, but if you let them they can build bridges.”
He still receives hundreds of secrets every week and admits he doesn’t know if he will ever be able to turn them off.
“It was an act of faith to ask for them,” he says referring to the initial art project idea.
“Everyone I talked to about it said I was crazy.
“Eventually the secrets did find their way to my mailbox. It was a slow trickle at first, but then it grew and grew. I realised I’d tapped into something that had been there the whole time, something that I don’t understand to this day which is full of mystery and wonder.
“My wife has a nightmare that in 30 years when we’re retired in Florida the secrets will still track us down.”
He’s not afraid of controversy – hosting an unmonitored forum on the website where people are able to add their reactions to the secrets he posts.
“There are sometimes good reasons to keep a secret secret,” he says. “They can be hurtful.
“The secrets that get the biggest negative reactions are secrets about pets and animals rather than horrific childhood experiences.
“Somebody said he gave his dog something bad to eat because he wanted to go back to see the veterinarian, who he thought was attractive. I got so many negative emails from people about that one.”
There are plans for a theatrical show based on the PostSecret phenomenon – something Warren describes as a cross between Rent and The Vagina Monologues.
But for now Warren sees the PostSecret Live show as the next natural stage for the project. He is creating a social space to share submitted postcards – and encourage people to step up to the microphone to share their deepest secrets.
“There can be such tension and release in the air,” he says. “It’s a totally non-anonymous way to take ownership of a secret and share it for the first time.
“My hope is that when people find the words for the first time they take ownership of a secret. Letting go of a secret allows them to reconcile with a part of their life in a new way.”
Warren shares some of his own secrets with the audience, as well as displaying some of the postcards he has received on the big screen – including those he wasn’t allowed to include in the books.
“I show secrets that have saved and changed lives,” he says. “Then I let people have that conversation, uncensored. It’s really the best part of the evening, when I stop talking and start listening.”
He admits his training as a counsellor on a suicide helpline comes to the fore, with his voice even slipping back into the tones he uses to answer the phone.
“Part of the training is to let people know you care what they are going through, listening to what they have got to say and letting them have as long as they need to say it,” he says.
“I have to remind myself at the events that when people share secrets they don’t want me to try and respond to them or solve a problem. Oftentimes being heard is enough.”
Brighton Dome Concert Hall, Church Street, Brighton, Monday, December 10. Starts 7.30pm, tickets £37.50. Visit www.tickettailor.com/checkout/view-event/id/4786/chk/e9c7