One of the best ways for anyone to survive the brutal winter in and around Leningrad during the siege is to be in possession of a pair of warm boots. The state of one's boots then becomes a way to identify the haves from the have-nots, and to make an educated guess as to who will live and who will die. Soldiers, both Nazis and Russian Red Army, are issued very warm and strong boots to withstand the hours they spend in the snow, while Lev notes that some of the Nazis' prisoners are barefoot, their boots stolen. If these prisoners can't survive the inevitable frostbite from walking barefoot in the snow, they'll certainly die of the cold and exposure. It becomes obvious then that boots aren't just about survival, they're also indicative of power. The Nazi soldiers had enough power to confiscate boots from their captives, while those still living in Leningrad have the power to steal boots from the dead. The blood on the boots for sale in the black-market Haymarket further serves as a chilling reminder of this power and of those who didn't make it.
The timeline below shows where the symbol Boots appears in City of Thieves. The colored dots and icons indicate which themes are associated with that appearance.
...Haymarket continued to thrive. Lev and Kolya walk through, taking in the stalls full of boots, pistols, grenades, and jars of dirt that came from under a bombed food warehouse, supposedly... (full context)