actually an important use case of this feature is to help writing domain specific language inputs, eg writing a python file inside D, or config / plain text files.
# is common in many languages (eg python/bash etc) as a comment.
@ would be inside string literal so should cause little confusion from D's side, but for example would force one to escape '@' in email addresses (more rare).
Frankly, this is bike shedding though; let's assume we pick one in
http://www.ascii-code.com/ and focus on whether we can agree on this feature.
I'm using it extensively for great benefit: more DRY code, less spurious files, cleaner integration with D.