Dear all
I hope I can shed some light on this. The inscription (left and right) means 'royal prince' or perhaps 'crown prince'. The object in the centre is a siamese crown. See also the following picture:
https://www.alamy.com/the-crown-pri...586386.html.In the bottom left corner is the (Siamese) number one. And in the right-hand corner is the currency denomination 'Sik' (1 Baht (Tical) = 4 Salung, 1 Salung = 4 Sik = 8 Sio = 16 Atts = 32 Solot). Based on this currency designation, this 'stamp' must have been issued before 1909.
I do not know whether this 'stamp' is a tax stamp, a fee stamp or a charity stamp. Or whether it is ultimately a pure 'fantasy issue' is for others to decide. But perhaps my findings will prompt someone who knows more about it.
Best regards from Switzerland
André