That chalked message

This is a map showing the tangle of alleys en route from Mitre Square to Goulston Street. Something slightly amusing about several of the narrow alleys called Hutchison. The killer could have discarded Eddowes’ soiled apron anywhere in these back streets

. But he didn’t. The killer wanted that apron found, which means he was making a declaration. Flinging down his gauntlet, alright in this case apron, and it served to underline that chalked message.