red mushroom
n.— «A preliminary investigation also found that the train’s braking system was not defective and that the operator did not press the “red mushroom”—Muni parlance for the bright red button on the operator’s console that activates an emergency brake. The light-rail vehicles are operated with hand controls.» —“Muni train likely speeding before crash” by Rachel Gordon San Francisco Chronicle (California) June 17, 2008. (source: Double-Tongued Dictionary)
Further reading
Aaron in Los Angeles, California, notes while using public transit in Britain he and other passengers were instructed to alight from the front, meaning “exit the car from the front.” Alight comes from an Old English word alihtan, literally, to...
Barb in Battle Creek, Michigan, reports that when she was a small child, a neighbor from Georgia said she would bring her a box with five handles for her birthday. Barb was overjoyed until she learned that the phrase is actually a joking euphemism...