Though the use of the word ‘hallmark’ may be permissible in the USA
and probably is used in many other countries, technically you are
only stamping or marking your work with your personal stamp and, if
you are using precious metals the requisite purity stamp. 925, 375,
585, 750 In Britain however, where hallmarking is still done after
mandatory purity checks at one of the ‘Goldsmith’ Halls’ where the
stamping is done. If work does not ‘come up to scratch’ it may be
crushed before being returned to you.
It would not be permissible to cast your purity mark in your work.
I am not sure of the latest rules as I live and work in Australia.
All gold over 1 gram and silver over 5 grams has to be posted to the
’hall’ where it is tested and marked.
There are penalties for violations and precious and other metals will
not be marked if they are soldered together and in that case, say,
silver cannot be called silver in a shop, it must only be called
white metal in any trade description.
Though this is an annoying, time consuming, and expensive exercise,
it was one of the first examples of consumer protection going back to
David Cruickshank (Australia)