A Frigid Jewel is a memento from Silent Hill: Shattered Memories. Harry Mason can find it in the biology lab of Midwich High School, inside a frog on a dissection table. Harry must cut open the frog to retrieve the memento, which is a ring with a blue gem, and it has the words "Ice Gem" written on the back.
The ring likely symbolizes Cheryl Mason's supposedly "frigid" behavior around her boyfriend Steve. Being found inside a frog's chest, it could also symbolize the cold heart of Cheryl's peers.