Platinum looks similar to silver but is worth significantly more. Other than a stamped inscription there is no quick method to 100% ensure the presence of platinum in a marketplace setting. Here are the best steps to help accurately identify platinum in your home.
First look for the most obvious signs by looking for the symbol "PT" on the inside of a ring or the back of a watch. If there are no markings on the back of a watch that you suspect might be platinum, open the back part of the watch and look for an inscription on the inside of the back cover.
Platinum has a very high melting point and will not discolour when exposed to heat like other metals. Place the jewelry in a metal spoon and hold it over a gas stove flame (use oven mitts to hold spoon). If the spoon changes colour and the jewelry piece does not than there is a high probability that it is platinum.
Purchase a test kit that uses acid to check for the existence of platinum. By rubbing a jewelry piece on a test stone you can then check for a reaction with a drop of acid on the metal residue streak. Platinum is very stable and will not react immediately to the acid drops like other metals. These test kits cost about $20.
Make sure to handle your acid kit with extreme care. Use appropriate protection (gloves, goggles) and keep it out of reach from children.