Unique jewelry pieces can be sold with a heavy price tag, especially if they have their original stamp or maker's mark. At JewelryWonder.com, you can set up an online store by uploading photos of pieces you own. If the jewelry was passed down by a relative or looks as if it's a few decades old, it might be just the thing costume jewelry enthusiasts are eager to get their hands on. Pieces by Trifari, a jewelry company popular in the '30s, can be distinguished by its trademark "T" stamp with a crown above it. Other sought-after pieces are Eisenberg Ice, especially pins made of Swavorski crystal (marked with "Eisenberg Originals") from the '30s.