Akhi Dom,
The letters Ha mim are derived from Quran, There are numerous letters in the Quran such as "Ha mim Sad" and many others that arent yet encrypted. Ha Mim is also a name of a Quranic Surah.
These are not to be mistaken with Ameen which has roots in all semitic languages.
This will explain more:
http://en.wikipedia.org/wiki/Muqatta%27at