here's my experience sometime last year regarding this topic...
not really intending to get a girl, just doing a quick "window shopping" at CWB on a lazy evening since i live nearby... then there came the police and saw me ringing some doors... asked if i speak cantonese, and when i said no, told me to get out
didn't really get out though... just went down and resumed the task quickly on the lower floors (as the cops are still on the top floors) before actually leaving
