The graffiti was a mix of symbols, phrases and company names.
"We've got bright orange 'USA' and dark red 'PG&E' and light blue 'Comcast,'" said Bob Fish. "We said, 'Geez.'"
The couple called PG&E to find out what was going on and discovered the paint was part of an ongoing project to replace decaying wooden street lights around town with newer metal ones.
That's all well and good, said Fish, but months later the graffiti was still there. So they called PG&E again.
"We said, 'Hey, what's the deal? You guys came out, you painted this stuff and now the paint is still all over the sidewalk,'" he said. "I mean, it really looks pretty bad."
Again the company promised to clean up the mess.
"But they didn't, they covered it over," he said.
The bright paint was covered with gray and black paint intended to match the color of the sidewalk and street. But it didn't quite match, said Fish.
And on top of it, the markings were now lit up by the newly installed street light.
"When we first started seeing it, it wasn't a big deal. But then we started seeing it at every single light post," Jennifer Fish said. "It's not just in our neighborhood; it's all over."
She's noticed it on Camino Tassajara, in front of John Baldwin Elementary School, and up and down Paraiso Drive, for instance.
"It's corporate tagging," she said.
The companies responsible for the "tagging" are PG&E - the contractor in charge of the street light replacement project - and a nonprofit service called USA, which stands for Underground Services Alert.
USA comes in whenever digging takes place to make sure the contractor doesn't damage cable or phone lines, or any other utility lines that are running below the surface.
The danger spots are marked with bright paint - a different color for each different utility company.
They're supposed to use temporary, chalk-based paint that easily washes off, and remove it once the project's complete, said Danville City Engineer Steve Lake.
"They don't always do that, but that's what they're supposed to do," he said.
Indeed, where the Fishes live near Contada Circle, as well as at some other locations around town, permanent paint was used instead.
PG&E spokeswoman Tamar Sarkissian apologized for the mistake. The cans with the chalk-based paint look similar to the regular spray paint cans, she said.
"What we're thinking is that possibly, by human error, somebody grabbed the wrong can," she said.
That's part of what concerns Bob and Jennifer Fish. The other part is that PG&E told them the project was expected to take 10 years to complete.
"We said, 'Wait a minute, are you telling me that for 10 years all our streets are going to be covered in graffiti?'" said Bob Fish.
Well, not necessarily. Sarkissian predicts it will take closer to five years.
Some of the street lights in Danville are owned by the town and others by PG&E. While the town has finished replacing its portion - about 500 street lights - PG&E's part is expected to take much longer.
"It is a long-term project but not as long-term as 10 years," Sarkissian said.
"If they continue to use the wrong paint, you can just see what the whole town of Danville is going to look like by the time we're done with this," said Fish.
He fears Danville's neighborhoods will turn into "West Coast reproductions of the Bronx."
But there's hope yet in avoiding such a fate. PG&E recently sent workers to Danville to clean up the paint, starting with Contada Circle, said Sarkissian.
"We have people out there right now with solvents and scrubbers," she said last week. "We're going through all the actions to make sure this is remedied, to make sure the neighborhood looks as beautiful as it did before."