When you complete this achievement, you receive the following in game mail from Jepetto Joybuzz:
Greeting and congratulations on collecting the full set of Dalaran coins! As a reward for all your hard work I have enclosed a freshly minted Titanium Seal of Dalaran. This is a special coin that we only grant to the most ardent of collectors.
I hope you enjoy this special reward, you've earned it!
- Patch 3.0.2 (2008-10-14): Added.