To answer the question, you need to know the legend of the Warsaw mermaid. Now I wrote information about her in the post, under the third photo. According to legend, the mermaid, who lived in Warsaw and sang beautifully on the Vistula River, was captured by a trader, and later freed by a good fisherman and promised him that she would protect him. That is why she was depicted on the monument in such a way - in symbols of protection - with a sword and a shield. It is also supposed to symbolically protect the inhabitants of Warsaw.