#{ in a few languages is a bit of a high-level operator like "start a record/object/hash table". The # is visually a bit like a handle on a coffee cup (which you are about to fill). The octothorpe (#) is also sometimes called a "hash", making it also a bit of a visual pun if it is indeed the start of a hash-table. (Think JSON object syntax in a language where you want to make sure you can't just accidentally write objects anywhere or confuse different uses of { such as starting a code block, so you put a handle on them.)

"Smushing" it together makes it even more visually distinct as a "single" operator, further adds to the visual metaphor of the "coffee cup handle", maybe obscures the "hash" visual pun a little bit, but maybe not enough to care.