Bowler hat
A bowler hat was a type of domed hat worn by the working class during the late 19th century.  It was also commonly worn on Sigma Iotia II during the 23rd century. 

Joe Falling Hawk, a Native American card shark who lived in San Francisco wore a bowler hat. Data later won the hat in a poker hand. ()

Numerous Iotian bosses, including Tepo, all wore bowler hats. ()

Geordi La Forge wore a bowler as part of his role as John H. Watson in Data's Sherlock Holmes Program 3A scenario. ()

External link 
 

Clothing