I just found the symbol ExpectationE
with autocomplete.
Rendered the symbol is
Searching the documentation and the internet leads to nothing. Does somebody know what this symbol does and what its purpose is?
It doesn't do anything, it just formats in a certain way. You can assign your own definition if you like.
References:
ExpectationE[x]
. $\endgroup$\[ExpectationE]
. It looks like the Rx recipe symbol used in pharmacy, but instead with an Ex. It is a script E joined to a small and subset x. $\endgroup$