These twin Siccae blades are twin Imperial Gold blades that belong to Meg McCaffrey. They are disguised as two rings that have sickle symbols, her mother Demeter's symbol, on them when not in use. How she got her blades is still a mystery.
Apollo asks about the siccae blades, but Meg firsts tells Apollo to stop, but later at the end of the book she tells him that the rings were given to her by her original father. In the Dark Prophecy Meg gets better at controlling the golden blades and is able to fight better.