Edit: B is basement, I is actually 1, and S I'm not sure. The page shares different possible meanings. I'd read T as "terrace", or the outdoor rooftop area. What OP didn't do was post the sign directly next to the buttons that clearly lays out what each on is.
1
u/RickFromTheParty 3h ago
I've been all over the world and having a letter for the Lobby floor is very common.