The city engineer shall, at the expense of the city, cause good and substantial signs bearing the names of the streets and avenues of the city respectively, to be put up and maintained upon at least two of the corners at each crossing of all streets and avenues. Such signs shall be so placed as to be in plain view of persons passing either way upon any of such streets or avenues. Where there are no buildings at or near such crossings or the streets or avenues are not open or graded, the putting up of such signs may be postponed until such time as it is deemed necessary or until it shall be directed by a resolution of the city commission. (Prior code § 4-4-8)