There is something very similar here: www.mamkft.hu/w_en_h_breed.php
Then scroll down to Mezohegyes Sports Horse. At the top of this page is a coat of arms and part of this resembles your drawing........ Hope this helps.
Nothing to do with the freeze mark but i was reading the msgs and i also have a horse out of GRANNUS.
It would be interesting to see what your horse looks like, if you have any photo's i would apretiate a look at them.....