The only special parameter variables that I am aware of are @Me, @MyGroups, @MyWorktree, and @Today which can be used in the CONDITIONS tab on the Generic Inquiry (SM208000) screen.
But it would be nice if we also had @Company and @Branch variables (or something like that).
Both @Company and @Branch would be needed because in 2018 R2 there aren't just Branches, but both Companies and Branches.
The Company/Branch that you have selected on the top doesn't mean that you're "logged in" to a Company or Branch. It's just a default value for any new transactions. This was made more clear in 2018 R2 by moving the selector to the top next to the Business Date which is also just a default value for any new transactions.
Even though the Business Date is just a default values for new transactions, the current @Today variable respects the Business Date.
So it would make sense to me that we could also have @Company and @Branch variables which respect the Company/Branch selector.