• There are no copyright marks on the card, as can be seen at the link above. The pages are clearly marked as advertisements, so they are not a part of any Popular Mechanics copyrights.
• US Copyright Office page 3-magazines are collective works (PDF)

"A notice for the collective work will not serve as the notice for advertisements inserted on behalf of persons other than the copyright owner of the collective work. These advertisements should each bear a separate notice in the name of the copyright owner of the advertisement."

• United States Copyright Office page 2 "Visually Perceptible Copies The notice for visually perceptible copies should contain all three elements described below. They should appear together or in close proximity on the copies.

1 The symbol © (letter C in a circle); the word “Copyright”; or the abbreviation “Copr.”

2 The year of first publication. If the work is a derivative work or a compilation incorporating previously published material, the year date of first publication of the derivative work or compilation is sufficient. Examples of derivative works are translations or dramatizations; an example of a compilation is an anthology. The year may be omitted when a pictorial, graphic, or sculptural work, with accompanying textual matter, if any, is reproduced in or on greeting cards, postcards, stationery, jewelry, dolls, toys, or useful articles.

3 The name of the copyright owner, an abbreviation by which the name can be recognized, or a generally known alternative designation of owner.1 Example © 2007 Jane Doe.")

本作品在美国属于公有领域，因为其于1930至1977年（包括）间在美国出版，且没有著作权声明。更多详情，请参见共享资源:赫特图表以及公共艺术品“出版”的详细说明。 请注意此作品在对美国作品不适用较短期限法则的管辖区可能仍然受版权保护（基于作者的逝世日期），例如加拿大（作者逝世后70年）、中国大陆（作者逝世后50年，不包括香港和澳门）、德国（作者逝世后70年）、墨西哥（作者逝世后100年）、瑞士（作者逝世后70年）及其他有本地条约的国家。 العربية ∙ беларуская (тарашкевіца) ∙ čeština ∙ Deutsch ∙ Ελληνικά ∙ English ∙ español ∙ français ∙ Bahasa Indonesia ∙ italiano ∙ 日本語 ∙ 한국어 ∙ македонски ∙ Nederlands ∙ português ∙ русский ∙ sicilianu ∙ slovenščina ∙ ไทย ∙ Tiếng Việt ∙ 中文（简体） ∙ 中文（繁體） ∙ +/−