what is up with all of the chalk "1700s" #s....

[brunoflipper]

what is up with all of the chalk "1700s" #s being written on structures in and around downtown... i noticed them starting last thursday...

they a written in 3-4 ft tall chalk script, the orange apartment building at 21st and riverside had 1727 written on it last week (i was erased the next day), every column on the 21st street bridge has 1729 written on it (on saturday), the fountain infront of the spirit bank building is labeled (as of today), the old railroad pedestrian bridge was labeled sunday morning, there was also a church and a building marked downtown last friday night... what gives?
anyone have any ideas?