A hallmark, by definition, is a mark or device placed or stamped on an article of trade to indicate origin, purity, or genuineness. With jewelry, this has come to mean the particular mark, normally either stamped or engraved, that indicates the individual maker of the piece. An item made in a shop by more than one hand, assembly-line style, will often have the mark associated with that particular shop or company. (Charles Loloma and Preston Monongye both worked this way, having inlay work done by other artists, but the current marketplace accepts these pieces as individually made because they were not done as multiples, as is the case with more modern shop artists like Ray Tracey.) However, there is another kind of shop mark that is distinctive to the Indian Southwest, where an individual artist would make a piece but only mark it with the shop mark. For collectors, this is a dangerous type of mark that can leave itself open to much misunderstanding and false conclusions.
A perfect example is the Thunderbird Shop, Frank Patania Sr.'s establishment in Santa Fe (and later Tucson.) From early in the history of the shop, silver produced there was marked with a stamped thunderbird to indicate its origin. Later, Patania put his own hallmark, a conjoined FP, on to his own pieces along with the thunderbird, while items made by other shop smiths, of whom there were many, would have only the thunderbird shop mark. Since Patania and the other smiths were all working off designs done by Patania, similar work was very common, and often the only true distinction between a Patania piece and a shop smith piece was the presence or absence of the FP. With the passage of time, it has become common for many pieces with just the Thunderbird Shop mark to be attributed to Patania, making them more valuable.
Some shops only used the shop mark, and the individual artists did not use their own hallmark--the Navajo Guild, for example, and the UITA posts. It is impossible to know exactly who made those pieces, but the shop mark serves as a clue to the origin and quality standards that were in place. However, with the Thunderbird (and the White Hogan, in Scottsdale), the shop mark was only part of the information. The accompanying hallmark is the true story, and all collectors and dealers should know how to read it.