Yeah, unfortunately a lot of software only supports the “Basic Multilingual Plane” of Unicode, and that includes Inform. So no emojis allowed.
But! There are a couple of musical note symbols that did find their way into the Basic Multilingual Plane, and can be used! The most widely-supported of these are Unicode 9834 (U+266A) for an eighth note ♪, and Unicode 9835 (U+266B) for beamed eighth notes ♫. So you can try those ones and see what the interpreter thinks! (9833 is a quarter note and 9836 is beamed sixteenth notes, but those are a lot less supported.)