A short time later, a sales assistant called the couple and told them to return to the store - where they were presented with the ring.
Walker had sought out the manager of the store and told him to put the ring "on his tab".
When the astounded couple asked who bought it for them, the clerks refused to say - at Walker's request.
The Uphams kept the gift receipt and often suspected it had been the star but could never be certain.
The store, which has since closed its Santa Barbara outlet, kept Walker's secret but after the 40-year-old's tragic death in a car crash on Saturday, employee Irene King felt the world should know the actor's true character.
Mrs Upham said Walker's gesture remains the kindest thing anyone had ever done for her.
She added: "His real life speaks volumes of his character. He really did put his money where his mouth is and did good for this world."
The Fast And The Furious star has been mourned by family, friends, co-stars and fans who laid a shrine to the star at the spot where he died in Santa Clarita on Saturday afternoon.
The 2005 Porsche Carrera GT was being driven by the Hollywood star's friend and business partner Roger Rodas when it crashed in Los Angeles, killing both of them.
On Monday, Walker's Fast & Furious co-star Vin Diesel joined crowds who'd gathered to pay their respects.
Speaking through a police car loudspeaker, he said: "If my brother were here right now and saw all the love that you're bringing here. If he could see for himself that all of you have showed up to show my brother love at this hard time. That his family gets to see all of you show the love that you've shown Paul. It's going to stay with me forever.
"I just wanted to say thank you. Thank you for coming down here and showing that angel up in heaven how much you appreciate him. It's going to stay with me forever."
- Daily Mail