To check a BIS hallmark online, you can use the BIS Care App or visit the official BIS website. Download the BIS Care App from the Google Play Store or Apple App Store, register your number, and go to the “Verify HUID” section. Enter the six-digit HUID number of your jewelry, and it will show you all the details like purity, jeweler’s registration number, and hallmarking center. Alternatively, you can also visit the BIS website and use the hallmark verification section for a quick check.