Section 19. Such notice shall be in writing, signed by the person injured or by some one in his behalf, and may be given, in the case of a county, to one of the county commissioners or the county treasurer; in the case of a city, to the mayor, the city clerk or treasurer; in the case of a town, to one of the selectmen or to the town clerk or treasurer. If the person injured dies within the time required for giving the notice, his executor or administrator may give such notice within thirty days after his appointment. If by reason of physical or mental incapacity it is impossible for the person injured to give the notice within the time required, he may give it within thirty days after such incapacity has been removed, and if he dies within said thirty days his executor or administrator may give the notice within thirty days after his appointment. Any form of written communication signed by the person so injured, or by some person in his behalf, or by his executor or administrator, or by some person in behalf of such executor or administrator, which contains the information that the person was so injured, giving the name and place of residence of the person injured and the time, place and cause of the injury or damage, shall be considered a sufficient notice.