2. The words in column 7 of Part I may be included in the lower half of the relevant sign shown in the corresponding entry in column 6 of that Part and where included shall conform in form and colour to those shown in the said column 7, except that—
(a)in the case of the signs for the classifications “non-flammable non-toxic gas”, “flammable gas”, “flammable liquid”, “spontaneously combustible substance” and “substance which in contact with water emits flammable gas”, any lettering may be in white;
(b)in the case of the sign for the classification “corrosive substance” the lettering shall be in white;
(c)in place of the word “toxic”, the word “poison” may be used wherever it occurs; and
(d)in place of the word “flammable”, the word “inflammable” may be used wherever it occurs.