Zyklon B was the name of the gas used to kill over a million victims, most of them Jews, in the death camps constructed by Nazi Germany during the Holocaust. Because of its association with killing Jews, Zyklon B has been adopted as a symbol by modern-day white supremacists, who often use it to make sick jokes about killing Jews.
The "echo," as it is sometimes called, is the on-line use by anti-Semites of multiple parentheses around a person's name to indicate that they are Jewish or, when used around a phrase or term, such as (((banker))), to imply that the word "Jewish" should be added to it.
ALTERNATE NAMES: Parentheses, Parenthesis
A common hand gesture that a 4chan trolling campaign claimed in 2017 had been appropriated as a symbol meaning "white power." Used by many on the right--not just extremists--for the purpose of trolling liberals, the symbol eventually came to be used by actual white supremacists as well. Caution must be used in evaluating instances of this symbol's use.