Strongsville police say the group gathered Saturday, and mall management asked three people standing on a table near a second-floor railing to step down. Kelly was among the three. When they refused, police were called.
Police say they're no longer in custody. Kelly tweeted later that "today was a statement."
Sean "P. Diddy" Combs told MTV this month that he signed Kelly, an Ohio native, to his Bad Boy Records label.
"Machine Gun" was the nickname of George Kelly, a Prohibition-era gangster.
The Plain Dealer reports that Cleveland's mayor recently vetoed an ordinance that would have criminalized some uses of social media and was aimed at curbing flash mobs.