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.
{{Information |Description=Postcard photo of the Denver and Rio Grande train "The Prospector", which traveled between Denver and Salt Lake City. |Source=[http://www.ebay.com/itm/Denver-Rio-Grande-Western-RR-5571-Streamlined-Prospector-/380453718890?pt=...