You should check the city or HOA (if one exists) codes on this. I don't believe Sierra Madre has a code preventing this so if that is the case all you can do is ask politely if they will consider moving them out of sight.
If there is zoning covering such a situation then you could have the zoning officer address the issue. In some places this would be covered in a deed, as something that would not be allowed.
In other cases there is nothing you can do.