Deanna "Violet" Maree CoCo, 32, was convicted and fined $200 after she admitted spray painting four yellow Woodside Energy logos on the front windows of the Perth Police Centre a day earlier.
Perth Magistrates Court was told CoCo was acting in solidarity with local campaigners targeted by police amid an escalating crackdown on protesters.
It included CoCo attempting to super-glue her arm to the window before police arrested and charged her with criminal damage or destruction of property on Wednesday.
Magistrate Matthew Walton said CoCo appeared to have "legitimate personal beliefs".
"It is noble and commendable people have strong personal views," he said on Thursday.
"It's a fundamental tenet of western democracy … a functioning democracy ... it should be supported.
"You don't have to go too far abroad to see the restrictions on personal freedoms and activism.
"In a lot of regards you should be commended, however, you breached the law ... you went too far on this occasion."
CoCo was ordered to pay $500 in damages.
"I encourage to you to do it but you should be encouraged to do it in a lawful manner," Mr Walton said.
"It should be something held to be very precious to all of us."
Outside court, CoCo said she was pleased to hear the magistrate say protest was an important part of a democracy but disappointed by police denying her bail and holding her overnight for "an art demonstration protest".
"We're still seeing that they are enacting their own justice ahead of the judiciary," she told reporters.
CoCo was among the first people charged after the NSW parliament hiked penalties and expanded the reach of laws targeting those who block traffic on major routes.
The NSW District Court in March wiped her 15-month prison sentence for parking a truck on the Sydney Harbour Bridge and blocking a lane during morning peak traffic in April 2022 as part of an environmental protest against climate inaction.
She was issued with a 12-month conditional release order after the court heard she had initially been imprisoned on false information from NSW Police.
"Here (in WA) the courts seem much more supportive of protesters, however, the police are clearly supportive of Woodside and their projects," she said.
Activist group Disrupt Burrup Hub on Wednesday said environmental campaigners have been subject to increasing police overreach in recent months in response to a campaign targeting Woodside's Burrup Hub project.
This has allegedly included house raids, data seizure and excessive charges after activists sprayed the Woodside logo on a famous Fredrick McCubbin painting at the WA Art Gallery and WA's parliament building.
CoCo said her actions on Wednesday were an attempt to "expose" the WA government's alleged use of the police force to protect Woodside from activist scrutiny.
Disrupt Burrup Hub has called for industrial development on the Burrup Peninsula, about 30km west of Karratha in the Pilbara region, to be stopped, including Woodside Energy's expansion of the Pluto gas plant.
"(It's) the largest new fossil fuel project in Australia and it's absolutely detrimental to our children's futures," CoCo said.
"Also, the (plant) is right next to beautiful Murujuga rock art that should be valued as one of Australia's most precious art sites as it holds women's law.
"We need to protect it."
The Burrup Peninsula, known as Murujuga to traditional owners, contains the largest and oldest collection of petroglyphs in the world.
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