first of all....I'm not saying the cops do this, just saying the technology could likely do it
guess it depend where you live and how eager the cops are and how cooperative the power company would be
if the cops did do this, I'm sure they would be more focused on large grow op's....600 watts is small potatoes
if this still worries you, then grow auto's at 24/0 (start to finish), then there is no cycle to detect
other alternative would be to frequently change the amount of power draw you have going on/off by adding a couple 23 watt CFL bulbs one day, none the next day, 13 watt bulb the next day, etc, or toggle on/off times by 2 or 3 minutes.... so any program looking for an exact repetition of power draw could be fooled