I think I finally found a Royal Cypher more or less matching the button.
It has the same number of vertical lines and the connecting curves seem to match.
It is Thai and has a very long link.
Next is to work out who was appointed crown prince ...
https://th.wikipedia.org/wiki/%E0%B8...%E0%B8%A1_2555
Here are Google's Royal Thai Cyphers:
https://www.google.nl/search?tbm=isc...r=1.25#imgrc=_