Why do some attributes start with '@' while others done't?

[Ola Fosheim Grøstad via Digitalmars-d]

On Friday, 22 January 2016 at 09:46:47 UTC, Jonathan M Davis 
wrote:
> Not using @ on any attributes would be far cleaner, but it 
> would eat up more keywords, and we arguably have too many of 
> those already.

D is too complex to defend the position that you need _reserved_ 
keywords. Maybe at some point in the past D1 was simple enough to 
defend that position.

You write a parser once or twice, so having a clean syntax weigh 
up for spending a little bit more time on the parser.

What D needs is consistent usage of sigils. It makes code easier 
to read and easier to write.

What does ":" mean? What does "@" mean? What does "!" mean?

No consistency in D.