The company's 1959 Rock and Roll cards and their TV Western series carried no company name or any copyright markings. These cards had blank backs, so many times when they're sold, the seller doesn't display the back. In this example both front and back of the card are shown.
Nu-Cards made other trading cards, sport cards among them. A check at copyright.gov for renewals/registrations found no record of the Nu-Card Company.
The card has no copyright markings on it as can be seen in the links above.
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.
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.
Cette œuvre est dans le domaine public car elle a été publiée aux États-Unis entre 1929 et 1977 inclus, sans indication de copyright. À moins que son auteur ne soit mort depuis suffisamment longtemps, elle n'est pas dans le domaine public dans les pays ou régions qui n'appliquent pas la règle du terme le plus court pour les travaux provenant des États-Unis, comme le Canada (cinquante ans pma), la Chine continentale (cinquante ans pma, Hong Kong et Macao exclus), l'Allemagne (soixante-dix ans pma), le Mexique (cent ans pma), la Suisse (soixante-dix ans pma) et d'autres pays signataires d'accord bilatéraux. Voir cette page pour de plus amples explications.