My friend lives on a flag lot in San Bernardino. Between the driveway and the neighbors blockwall is a slope owned by the neighbor. This slope is always overgrown with weeds. She has already had a discussion with the neighbor about their weed situation. The neighbors are not able to see the unsightly mess from their front yard, (which is, incidentally, beautifully manicured) nor do they use the driveway.
The last time She spoke to them and asked them to weeds on the slope, they grudgingly complied, but she don't think it should be up to her to be policing this every few months.
She very concerned about them turning into a fire hazard in the summer.
Image courtesy of:hawaiilife.com/articles/2011/06