Identifying a Vintage WWII Pearl Necklace: Hallmark & Maker Information

Question
My wife has a pearl necklace that was given to her by her grandfather. He purchased this strand while in Hawaii during WWII. We are trying to determine the manufacturer. The necklace is 18", with a button clasp with matte gold finish with a pearl inset. The only distinguishable mark is a gold cursive "D" hanging from the clasp. Any ideas on who made them or even an idea how we can find out? Any help would be appreciated.

Answer
This is a Hallmark or Makers Mark. There are many of these so it is very difficult to be able to Identify them.
Try checking with jewelers and manufactures in your area for there Hallmarks and see if they match.
If it was an "M" It might be Mikimoto or maybe Maijorka
You can also check with various hallmark publications as well as searches for jewelry hallmarks.
Good Luck,

Sincerely,
Arthur DeMello GG (GIA)
A. DeMello Gemological Laboratory
http://www.jewelryappraiser.info