Jamieson, Fausset and Brown on Ezekiel 39:15

15. First "all the people of the land" engaged in the burying for seven months; then special men were employed, at the end of the seven months, to search for any still left unburied. The passers-by helped them by setting up a mark near any such bones, in order to keep others from being defiled by casually touching them, and that the buriers might come and remove them. Denoting the minute care to put away every relic of heathen pollution from the Holy Land.