(b) The words "owner or operator," as applied herein to railroad companies, shall include every railroad company incorporated by or under the laws of this state for the purpose of constructing and operating a railroad, or of operating part of a railroad within this state, whether the railroad or any part of it be in operation or not; and shall also include every other railroad company, or persons or associations of persons, owning or operating a railroad or part of a railroad in this state on which freight or passengers, or both, are carried for compensation. The word "railroad," as used herein includes every street, city, suburban or electric or other railroad or railway.
(c) The words "owner or operator," as applied herein to express companies, shall include every express company incorporated by or under the laws of this state, or doing business in this state, whether incorporated or not, and any person or association of persons, owning or operating any express company or express line upon any railroad or otherwise, doing business partly or wholly within this state.
(d) The return shall be signed and sworn to by the owner or operator if a natural person, or, if the owner or operator shall be a corporation, shall be signed and sworn to by its president, vice president, secretary or principal accounting officer.
(e) The return required by this section of every owner or operator shall cover the year ending on the thirty-first day of December, next preceding, and shall be made on forms prescribed by the board of public works, which board is hereby invested with full power and authority and it is hereby made its duty to prescribe the forms as will require from any owner or operator herein mentioned information as in the judgment of the board may be of use to it in determining the true and actual value of the properties of the owners or operators.