The billboard, which is located on LA's Sunset Boulevard, features von Anhalt and Gabor's wedding picture as well as the caption: "Prince Frederic & Princess Zsa Zsa 25 years and counting."
Von Anhalt told The AP: "The billboard was very expensive. I just put my life savings in it. I said forget about tomorrow. I want to do it today. I want to do it for her."
He added: "Being married to Zsa Zsa these 25 years, it's priceless. What she gave to me, the things we did together, the happy life we had together, you can't pay for it with money. It was perfect. It was just perfect and we're going to go on."
The couple's billboard, which also features von Anhalt's website address, will be displayed in LA for the next month.
Von Anhalt said that he will also throw a silver anniversary party in August, where each guest will be allowed a private visit with Gabor in her bedroom.
Gabor has battled a variety of illnesses in the last several years and most recently fell into a coma while hospitalised for a stomach illness. She awoke from the coma a week later and was eventually allowed to return to her home.
Von Anhalt revealed that Gabor's condition has remained stable since her most recent hospitalisation.
Gabor and von Anhalt wed on August 14, 1986. The Moulin Rouge actress has been married nine times in total.
> Zsa Zsa Gabor's husband 'hits van with car'
Watch the unveiling of Zsa Zsa Gabor and husband Frédéric Prinz von Anhalt's billboard below: