The Companies Act 2013, specified the contents of a Letter Head, bills or other official communications. As per the section its should contain full name, address of its registered office, Corporate Identity Number (21 digit number allotted by Government), Telephone number, fax number, email id, website address  if any.

Requirements as per Section 12 (3) of the Companies Act, 2013

That Every company shall—

(a) paint or affix its name, and the address of its registered office, and keep the same painted or affixed, on the outside of every office or place in which its business is carried on, in a conspicuous position, in legible letters, and if the characters employed therefore are not those of the language or of one of the languages in general use in that locality, also in the characters of that language or of one of those languages;

(b) have its name engraved in legible characters on its seal;

(c) get its name, address of its registered office and the Corporate Identity Number along with telephone number, fax number, if any, e-mail and website addresses, if any, printed in all its business letters, billheads, letter papers and in all its notices and other official publications; and

(d) have its name printed on hundies, promissory notes, bills of exchange and such other documents as may be prescribed

Sub section (8) If any default is made in complying with the requirements of this section, the company and every officer who is in default shall be liable to a penalty of one thousand rupees for every day during which the default continues but not exceeding one lakh rupees