You mean D "three quarter" sharp? The name is a bit illogical because it's really "a sharp and a half", or "sharpened three quarters of a tone". The usual representation looks like a sharp with three vertical bars, and there's a unicode symbol for it (tried to cut and paste but no luck). Microtonality is really annoying on a piano though.

As it happens I've been trying to work out what exact intervals are used for the two-chord leitmotif heard in "The Sandman" series, I'm not sure if they're regular microtones or just some sort of eerie detuning (surprisingly I can't find any discussion of it online either).

I meant to ask regarding D-sharp and E-flat, but a typo led me to learn about microtonality. Bravo and thank you!

the sandman (*) intervals aren’t coming from microtonal tuning… it’s dynamically modulated detuning in equal temperament, just as you say. it’s an extremely common type of modulation, especially if there are synthesizers involved.

* what an incredible show!