Is this weird "such that" notation valid? I've seen that the phrase "such that" can be notated as a $|$ or  a $:$, specially when you are using a set builder notation. My Geometry teacher also occasionally uses an $\in$ but "backwards" when stating theorems.

But now my Calculus teacher uses a weird symbol that I've never seen before. It's like an normal uppercase E, but "laying down", "rotated -90°", or like three parallel vertical lines with a horizontal line over them, like this:



Does this symbol even exist?
Have you seen it before? Where?
Is it correct to use it?

Thanks.
I've searched over 900 symbols using this tool and I wasn't able to find such one, nor have I ever seen it used.

My advice would be to just ask your professor if he invented that symbol, and if he did, for what reason.
I've seen it used before, not sure where. Doesn't seem to have caught on. It's $\ni$ = "\ni". See this tex question.