Tracy Faust, 41, mounted a taxi sign on the roof of a white Cadillac on Oct. 16 to pick up a University of Georgia student downtown, then drove him to East Athens and robbed him at gunpoint, police said.
Faust landed in jail a week later, charged with armed robbery and other crimes.
Although Faust remains in the Clarke County jail without bail, someone used the same trick to rob another "fare" early Saturday morning, according to police.
That makes investigators think Faust might be friends with people who continue to use the same taxi sign.
"We know that Tracy used a taxi sign, but we haven't recovered it," said Athens-Clarke police Capt. Clarence Holeman, the commanding officer of Centralized Criminal Investigations.
"We haven't ruled out the possibility there's a copycat, because there could be someone out there with that sign and still trying to use it," Holeman said.
Legitimate cab companies have to meet a list of local requirements to protect the driver and passengers - such as marking the vehicles with the company name - but police regularly warn downtown bar-goers to look out for criminals posing as cab drivers.
In last weekend's robbery, an Alpharetta man who had been drinking downtown climbed into a champagne-color Cadillac he thought was a taxi early Saturday, police said.
After he got in, a man in the front passenger seat removed a taxi sign from the car roof and put it on the floor, police said.
The men drove the victim to a convenience store at North Avenue and Martin Luther King Jr. Parkway, where the driver pulled a semiautomatic pistol and demanded money, police said.
The robbers left the man standing outside the store and drove away toward downtown with his cell phone and $10 from his wallet, police said.
The victim described the robbers as black men in their early to mid-20s, one with dreadlocks and wearing a red hat, the other clean-cut with short hair, according to police.
Both times, the victims might have been easier targets because they'd been drinking, according to Holeman, who said a sober person might have sensed that something wasn't right even though the car had a taxi sign on the roof.
"The only thing we can do is keep trying to educate people and teach them they need to take responsibility for themselves," he said.
Local law requires that taxi cabs bear the company name and telephone number, have posted fare rates and a light on the roof. Drivers must carry photo ID.