[quote=Deathdaeg]
I was using it as the letter 'D', since the in 'Dah' is represented by a separate letter.
[/quote]

No the "ah" is technically apart of the letter sound. Like "Duh" is the sound for our D. But I get what you're saying. If the word was "Dah" you wouldn't just use the letter D. 
What I was asking really was what the significance was.