The real platinum necklace will definitely be printed with the logo of "PT", and 950 is purity. Without this logo, it must be fake platinum.
However, there is no guarantee that the PT logo will be 100% authentic. Pure platinum is white and shiny, while platinum is beige and silver is white. You can see if there is a certificate. General platinum jewelry will be equipped with relevant certificates to prove the authenticity of its platinum. If there is no certificate, you can't buy it.