The bird on the seal is a magpie. The music played whilst Moriarty was breaking into the Crown Jewels is 'The Thieving Magpie' (La gazza ladra) by Rossini. Magpies, and their near relatives, like to steal and hoard bright shiny objects. They also raid nests and eat eggs and baby birds.

The one with what looked like sawdust was filled with crumbs. This is a reference to Hansel and Gretel which is a theme running throughout the episode.

The book is another reference to Hansel and Gretel, bearing in mind that it is a young brother and sister who are kidnapped (as in the story) and they are taken to a sweet factory (in the story it is a gingerbread house of the witch who then imprisons Hansel in order to fatten him up whilst Gretel is used like a slave). The book is a clue.