From what I have seen on History Channel’s “Gangland”, when someone leaves a gang (or thrown out), scissors or a sander is used to remove the tattoo.... forcefully. Inking over it isn’t an alternative.
"Typically a gang tattoo, the teardrop is regrettable for two reasons. This small tattoo makes the wearer appear to be crying. Why? Because in America, the teardrop signifies the wearer murdered someone. So the first layer of regret is in the remorse the wearer feels for his misdeed. But the second form of regret comes when the wearer wakes up one morning and thinks to himself, "Wait a second, everybody in the whole world now knows that I'm a killer. Just because of this stupid little teardrop on my face." Then the real regret sinks in. Imagine one of these teardrop ex-killers on a job interview. I wouldn't even want to take a spicy chicken sandwich from one of these guys at Wendy's. Interestingly enough, in Australia, the teardrop means something totally different. It is inked onto child molesters in prison against their will in order to mark them for regular beatings and rapes. Talk about regret."