(CNN)"Slaughtered in school"
"And still no gun control?"
"How come, Marco Rubio?"
That's the message scrawled across three mobile billboards seen Friday near Sen. Marco Rubio's office in Doral, Florida.
The moving missive aims to call out Rubio just days after a gunman with what police say was an AR-15-style rifle stormed a high school in Parkland, Florida, leaving 17 people dead. Its placard trio borrows from the Oscar-nominated movie, "Three Billboards Outside Ebbing, Missouri," about a mom who rents road ads to call attention to her daughter's unsolved murder.
Avaaz, an online activist group, created the campaign targeting Rubio, which also was spotted rolling through downtown Miami and Little Havana.
"Florida has notoriously lax gun laws, and Rubio, who is supported by the NRA, has never attempted to reform them," Emma Ruby-Sachs, Avaaz's deputy director said. "The senator ranks as one of the highest recipients of NRA contributions and has received an A+ rating from the NRA."
Rubio, a Republican who ran for president in 2016, said Thursday that gun restrictions would not have prevented the mass shooting at Marjory Stoneman Douglas High School. The senator had received $3.3 million from the National Rifle Association as of October, according to The New York Times.
A person who answered the phone Friday at Rubio's Miami-area office declined to comment on the billboards.
Added Ruby-Sachs: "Today citizens are asking: How come Rubio refuses to protect our children? The senator has taken fire across the country for his toothless response to the shooting, calling it 'inexplicable'. We called (that) 'inexcusable.'"