The "KRAMER STERLING" stamp confirms that this specific rhinestone skeleton key brooch was manufactured by Kramer Jewelry Creations (often known as Kramer of New York). 

Historical & Collectible Insights

• The Era: While the company primarily produced heavily plated base-metal costume pieces throughout its history (1943–1980), it released a dedicated line of fine .925 sterling silver jewelry during the 1940s. This restriction was largely due to wartime metal shortages that limited standard base metals. 

• The Maker: Founded by Louis Kramer in New York City, the company became renowned for its high-quality, brilliant, prong-set Austrian crystal rhinestone work. 

• Value & Collectibility: This exact key design is a documented Kramer novelty piece. Having the "Sterling" stamp makes it rarer and more desirable to vintage jewelry collectors than their standard rhodium-plated versions

• The Sterling & Kramer Premium: Because your specific brooch carries the coveted "KRAMER STERLING" hallmark, it commands a higher baseline. Similar signed Kramer key brooches generally retail on platforms like Etsy or eBay in the $35 to $40 range. If it is in absolutely flawless condition with a highly motivated collector, it can peak near $65