Publisher:Signet

Signet is an Imprint of the New American Library (NAL). Since NAL were acquired by Penguin in 1987, "Penguin/Signet" books have appeared.

Usual ISBN prefix 0451.

Catalog numbers and price coding

 * Up to 1958 Signet used just a number for their catalog number. If they reprinted at a higher price they used a new number. The range of numbers issued for each year has not been researched.
 * Between 1958 and 1961 Signet started using a letter prefix to indicate the price. The numbering continues as before.
 * s ### - 35¢ (lower case s)
 * D ### - 50¢
 * P ### - 60¢
 * T ### - 75¢
 * Y ### - $1.25
 * W ### - $1.50
 * E ### - $1.75 or $2.25 (need more data, $1.75 is more likely)
 * Some imprints had a letter in front of the price code
 * Cx ### - Signet Classics. The "x" is the price code. For example CQ494 is a Signet Classic book priced at 95¢.
 * Kx ### - Signet Key. The "x" is the price code
 * In 1968 Signet started coding the catalog number on the spine as 451-x###-zzz where x is the price code, ### is the catalog #, and zzz is the price.
 * In 1977 Signet dropped the catalog numbers and started using ISBNs. The incrementing catalog number continues to be used.
 * In 2007 Signet started using ISBN-13. The incrementing catalog number continues to be used and is up to the 22000s.