The United States Mint issues annual Proof and Mint sets exhibiting coins released that year. Different varieties and errors can be found among many of these collector sets. In 1979 - toward the end of production when mint marks (single-letter indicators of where a coin was produced, such as “S” for San Francisco) were still being hand-punched - a decision was made to change the mint mark design on the dies (the two metallic pieces used to strike the sides of a blank coin planchet, giving the coin its unique image). Although the variances between the 1979 S Mint Marks are subtle, the value between the two can differ quite significantly.
The Type 1 Mint Mark, which is rather blurry, is commonly referred to as the “Filled S” because the inner part of the loops of the “S” are quite unclear and hard to distinguish. In crude terms, the Type 1 Mint Mark resembles an S-shaped blob with the tips of the “S” (or the serifs) flattened and lacking definition. (An interesting fact: This type was also used for the 1979 S Business Strike Susan B Anthony Dollars. Business Strike simply implies that the coin was intended for circulation, otherwise known as “everyday use.”)
In contrast to the Type 1 Mint Mark’s inclination toward an S-shaped blob, the Type 2 Mint Mark’s “S” appears more defined and distinctly featured. The inner part of the loops of the “S” are quite visible. Thus, it is often referred to as the “Clear S.” The serifs of the Type 2 “S” are well rounded and look “bulb-like.” In most cases, this “S” type appears to be raised above the coin surface with definite ridges, rather than sunk into the coin like a Type 1 Mint Mark.
When determining which type a 1979 San Francisco minted coin is, always keep in mind the possible history and situational wear that a coin may have experienced. If the coin has never been circulated or damaged, yet, it is difficult to determine what type it is, one issue could be that the original die used to strike the image into the coin was worn and faded at the time of production. This would cause a Type 2 Mint Mark “S” to appear less defined or clear and mistakenly categorized as a Type 1 instead. Other issues that complicate discernment can easily be corrected by taking great care to observe the “S” serifs, which are always a good identifier. It is imperative for a buyer or a seller of coins to be able to note the differences because there exist fewer Type 2’s (than Type 1’s) and they tend to carry a far larger premium. Below are detailed examples of each Type’s mint mark per denomination.