No sign shall be attached to trees, fence posts, stumps, utility poles, bridges, culverts or other signs, but shall be free standing or attached to buildings in an approved manner, except this restriction shall not apply to legal notices and public announcements to advertise public benefits of churches, fire companies, other public charitable or religious events and, also, public sales of an individual's household goods, farm equipment, or property are permitted providing that (a) the notices are not posted for more than three weeks prior to the event and (b) the notices are removed within 48 hours following the event.