A hallmark is a tiny stamp printed on solid gold jewellery to certify its purity.

Your item may have a single hallmark (ie '9ct' or '375') or multiple hallmarks.

Some countries use 'kt' instead of 'ct'. The higher the carat weight, the higher the gold purity (& the more valuable your gold).

Rings
Take a peek at the inside of the band.

Necklaces
Check the necklace clasp or pendant.

Bracelets
Take a peek at the bracelet clasp.

Earrings
Look at the posts or the backs of studs.