A friend has kindly supplied some further information:
The “Crown” is a tax mark of the “CapitanÃa General de Guatemala” (Supreme Command of Guatemala; until beginning of the XIX century elected by the Spanish kings). It’s signification is, that has being paid the “impuesto del quinto” (tax of the fifth of the value of the item in question). Source: Josefina Alonso, El arte de la platerÃa en la CapitanÃa General de Guatemala. 1981
Explanation of the Guatemala Assay Mark:
It was provided by the “CapitanÃa General de Guatemala” (who's residence was in 1524 first time moved to “Santiago de Goathemala”. In 1541 a mudslide and an earthquake destroyed that capital. So in 1543 until 1773 the “CapitanÃa” of all Spanish Crown related area in Central America was settled in a newly built town in a valley not so far away.)
That 3rd capital was in 1566 decorated by the Spanish king Philip II with the name “La Muy Noble y Leal Ciudad de Santiago de los Caballeros de Goathemala” (The very noble and loyal city Santiago of the Knights of Guatemala).
The Punch show (normally) a knight, brandish his sword on a to the left galloping horse, jumping over the two neighbors’ volcano’ of the 3rd capital of Guatemala, “Agua” (water) and “La Horqueta”, a Gemini of “Acatenango” and “Fuego” (fire).
There are existing many incomplete struck versions; e.g. as the here shown ones. But almost all could be recognized by an animal jumping over two “peaks” (of volcano’). So the remark of “salmoned” on what it is, is answered.
In summer 1773 an earthquake has destroyed that 3rd capital of Guatemala, today called “Antigua Guatemala” — and it seems that that time range was also the end of use of this punch?
Source: Alejandro FernÃ¡ndez, Rafael Munoa, Jorge Rabasco, EncyclopÃ©dia de la Plata EspaÃ±ola y virreinal americana. 1984, p. 510-512.