The couple, who got engaged on The Bachelor's season finale, posted photographs online of a walk on Baker Beach.
Flajnik added a caption explaining that the pair had seen a wedding ceremony being set up on the sand.
"Should we get married here? ;)" he wrote. "A picture of @bugrobertson and I observing a wedding at Baker beach in San Francisco. [My dog] Scotch is pooped from running all day."
Meanwhile, Robertson uploaded a picture showing Flajnik and Scotch running along the beach.
"I love this candid photo of my boys playing at Baker Beach this morning!" she said. "I am in love with this place, first time here. I think this would be a fun place for a wedding @BenFlajnik ;)"
The pair's hints came just a day after Flajnik had tweeted that Robertson was in San Francisco for their engagement dinner.
"Engagement dinner tonight in San Francisco with the little lady @bugrobertson and some wonderful friends we have made along the way," he said. "Man, what a ride."
Earlier this year, Flajnik and Robertson explained that they were in no rush to marry, saying that they were "engaged dating".