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Oh, but of course $\emptyset$ comes from Bourbaki. Interestingly, so does $\Rightarrow$ to denote implication, and $\in$ instead of $\varepsilon$. The "Dangerous bend" comes from Bourbaki as well.
However, my all time favorite is the set of associated primes of a module M. $Ass(M)$ is in fact called the assassinator of $M$, and its elements are called assassins.