For years I wondered why the backs of Westclox alarm clocks listed patent dates at first, then were changed in 1927 to show patent numbers. Recently I was reading a book about vacuum tube history [Saga of the Vacuum Tube by Gerald F. J. Tyne, 1977, p. 283], and found:

“In April 1927 the U.S. patent law was revised and required that the patent marking on any article made under a patent issued after that date should consist of the patent number rather than the date of issue, as heretofore. An article made under patents issued prior to the effective date of change in the law could be marked with either the date of issue or the patent number.”

Stamping patent numbers instead of dates on the backs of clocks makes sense for the following reason. When one searches by a patent date, there may be many results for that date; but each patent number has a unique patent. 

The pictures below show examples of the change from patent dates to patent numbers in the Big Ben Style 1a and the Baby Ben Style 1.

The following pages on the clockhistory website list some back types of Big Ben and Baby Ben alarm clocks:

Big Ben Style 1a Back Types
Big Ben Style 2 Back Types
Baby Ben Style 1 Back Types
Baby Ben Style 2 Back Types

History of the Patent Marking Requirement

I found a document giving a brief history of patent marking requirements [Santa Clara High Technology Law Journal, Volume 11, Issue 2, Article 1, January 1995, Patent Marking of Systems, Carl Oppedahl].

“The earliest patent statutes imposed no duty on a patent owner to mark articles. All persons were “bound to take notice of their contents”. The Patent Act of 1842 required the patent owner to mark each product with the date of the patent, and failure to do so would result in a fine of not less than one hundred dollars. The Patent Act of 1861 changed the marking requirement, eliminating the fine for failure to mark and instead establishing a rule much like today’s rule, where failure to mark relieves an infringer of liability for conduct prior to the date of actual notice. The Patent Act of 1870 left the 1861 marking rule substantially unchanged, as did the Act of 1927. The 1927 Act did, however, change the required mark to the word “patent” and the patent number. The marking provision of the Patent Act of 1952 left the marking requirement largely unchanged except to permit the abbreviation “pat.” in place of “patent”.”

The 1927 Patent Law

The 1927 patent law [SIXTH-NINTH CONGRESS. Sess II. Chs. 66, 67. 1927. pp. 1058 – 59] says:

“February 7, {1927, H. R. 7563.} {Public, No. 580.}”

CHAP. 67.—An Act To amend section 4900 of the United States Revised Statues.

“Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled, That section 4900 of the Revised Statutes of the United States shall be amended to read as follows:

“It shall be the duty of all patentees and their assigns and legal representatives, and of all persons making or vending any patented article for or under them, to give sufficient notice to the public that the same is patented; either by fixing thereon the word ‘patent’ together with the number of the patent, or when, from the characteristics of the article, this can not be done, by fixing to it, or to the package wherein one or more of them is inclosed, a label containing the like notice: Provided, however, That with respect to any patent issued prior to April 1, 1927, it shall be sufficient to give such notice in the form following, viz: ‘Patented,’ together with the day and year the patent was granted; and in any suit for infringement by the party failing so to mark, no damages shall be recovered by the plaintiff, except on proof that the defendant was duly notified of the infringement and continued, after such notice, to make, use or vend the article so patented.”

“Approved, February 7, 1927.”

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