This might be a silly question, but is there any standard notation for a binary relation $\square$ such that for any two sets $X$ and $Y$, $X \square Y$ iff there is a bijection between $X$ and $Y$?
I cannot recall if I have ever seen a notation like this. Straightforward googling gives no results either.
(Of course, the need for this notation can be overcome easily in a variety of ways – I am just curious if an appropriate symbol for a binary relation exists as well).