Miami Vice

While working an undercover prostitute sting operation in a nightclub to arrest a pimp named Neptune, Miami-Dade Police detectives James "Sonny" Crockett and Ricardo "Rico" Tubbs receive a frantic phone call from their former informant Alonzo Stevens (John Hawkes). Stevens reveals that he's leaving town, and, believing his wife Leonetta to be in immediate danger, asks Rico to check on her. Crockett learns that Stevens was working as an informant for the FBI but has been compromised. Crockett and Tubbs quickly contact FBI Special Agent in Charge John Fujima (CiarÃ¡n Hinds) and warn him about Stevens' safety. Tracking down Stevens through a vehicle transponder and aerial surveillance, Crockett and Tubbs stop him along I-95. Stevens reveals that a Colombian cartel had become aware that Russian undercovers (now dead) were working with the FBI, and had threatened to murder Leonetta via a C-4 necklace bomb if he didn't confess. Rico, learning of Leonetta's death by telephone call, tells Alonzo that he doesn't have to go home. Hearing this, the grief-stricken Stevens commits suicide by walking in front of an oncoming semi truck.
En route to the murder scene, Sonny and Rico receive a call from Lt. Castillo (Barry Shabaka Henley) and are instructed to stay away. He tells them to meet him downtown, where they are introduced in person to John Fujima, head of the Florida Joint Inter-Agency Task Force between the FBI, the DEA, and ICE. Crockett and Tubbs berate Fujima for the errors committed and inquire as to why the MPD wasn't involved. Fujima reveals that the Colombian group is highly sophisticated and run by JosÃ© Yero (John Ortiz), initially thought to be the cartel's leader. Fujima enlists Crockett and Tubbs, making them Organized Crime Drug Enforcement Task Force deputies, to help, and they continue the investigation by looking into go-fast boats coming from the Caribbean, delivering loads of narcotics from the Colombians. They then use their Miami informant contacts to set up a meet and greet with the cartel.
Posing as drug smugglers, Sonny and Rico offer their services to Yero, the cartel's security and intelligence man. After a high tension meeting they pass screening and are introduced to Arcangel de Jesus Montoya (Luis Tosar), South Florida's drug trafficking kingpin. In the course of their investigation, Crockett and Tubbs learn that the cartel is using the Aryan Brotherhood to distribute drugs, and is supplying them with state-of-the-art weaponry (which they had used to kill the Russian undercovers). Crockett and Montoya's financial adviser and lover Isabella (Gong Li) begin a secret romance and Tubbs begins to fear for the team's safety. Those fears are soon realized as Trudy (Naomie Harris), the unit's intelligence agent and Rico's girlfriend, is kidnapped by the Aryan Brotherhood by Yero's order, who never trusted Crockett and Tubbs. The Aryan Brotherhood demand for Crockett and Tubbs to deliver the cartel's load directly to them. With Lt. Castillo's help, the unit triangulates Trudy's location to a mobile home in a trailer park and perform a rescue, but she is critically injured when Tubbs fails to evacuate her before a bomb is remotely detonated by Yero. Soon afterwards, Yero reveals Isabella's betrayal to Montoya and captures her. In the showdown, Crockett and Tubbs face off against Yero, his men, and the Aryan Brotherhood at the port of Miami.
During the firefight, Crockett begins to call in backup. When Isabella sees his police shield and radio, she realizes that he's undercover. Betrayed, she demands that Crockett tell her who he really is. After the gunfight, Crockett takes her to a police safe house and tells her she will have to leave the country and return to her home in Cuba. Meanwhile, Tubbs is keeping watch on Trudy in hospital, and she begins to recover.

Question: How does Isabella understand Crockett is actually a policeman?
Answer: When Isabella sees his police shield and radio, she realizes that he's undercover.; When Isabella sees his police shield and radio, she realizes that he's undercover.