TLDR nevermind I'll include a screenshot;
I've looked for the symbol everywhere, it wasn't even found via wikipedia:
https://en.wikipedia.org/wiki/List_of_logic_symbols
It also wasn't in the list of mathematical symbols: https://en.wikipedia.org/wiki/List_of_mathematical_symbols
There's a section called 'advanced and rarely used logical symbols' in the wiki page for logic, and it's not even there. So that is officially the point at which I give up.
I don't mean the symbols for True, T. The stem of the T by the way, remains untouched, it's just that the left side is 'cut off'.
Also, I would copy and paste the damn thing, but it's always added in via a super special way, and it just turns out like this: f Γ. So yeah.
Best Answer
In Sequent Calculus discussions, capital greek letters such as $\Gamma, \Delta, \Sigma,$ and $\Pi$, are often used as symbols for finite sets of first order predicate logic formula. (Pronounced "gamma", "delta", "sigma", and "pi".)
https://en.wikipedia.org/wiki/Sequent_calculus#Inference_rules
In this case the rule of implication introduction, means that "if some set of formula and $A$ entails $B$, then that set of formula entails that $A$ implies $B$." $${\begin{array}{rcl}\Gamma, A & \vdash & B \\\hline \Gamma&\vdash&A\to B\end{array}}{\small{\to}\mathsf I}$$