Does anyone recognise this necklace?

[Hanniball]

Hello everybody!

I am creating this thread to find out what kind of necklace/medaillon/charm I have or actually... had...

A few years ago I inherited this necklace from my granddad. My granddad got this necklace as a gift about 20-30 years ago in Japan.

A month ago I brought it to a jeweler to make a repair on the lock.. and now they are telling me its lost.. therefore I would like to find out what the message/origin is of this necklace.

My grandmother told me it has something to do with being older than 50 years old. I personally think its something like a constellation, Dragon in this case.

The necklace:
It is a gold round medaillon/charm
In the center is pictured a japanese dragon
Around it looks like a rope kind circle around it

Hopefully someone is able to help me, I would really appreciate any suggestions!