Not sure what "platinum" has to do with the price of eggs in China.... but :P
Actually... I sorta overstepped with that statement... I should have been more specific... ITS illegal to sell jewelry made of any precious metals without some sort of mark OR paperwork BY the manufacturer... SO this is why it is RARE to see precious metal jewelry without markings.
This is and has been standard in the industry for eons... since at least 1900 I think.
"Jewelry manufacturers in the United States must inform the consumer about precious metal content, but the content doesn't actually have to be stamped on the piece. It can be on the appraisal accompanying the item, on a hang tag or packaging component, or on the invoice or receipt for the purchase".
These are the "exceptions".
There are no legal stamping requirement for non-precious metals.