Hallmarking can be done fairly easily and is a legal requirement if you intend to sell your work and it is over the minimum weight (currently silver over 7.78g, gold and palladium over 1g, and platinum over 0.5g). More information can be found on the London Assay Office website or speak to one of our members – many of us have our own hallmarks and can tell you how to go about getting one and getting your work hallmarked.
For further information you can also have a look at The Goldsmiths Company.