Hard Case Crime

Hard Case Crime is an American imprint of hardboiled crime novels founded in 2004 by Charles Ardai and Max Phillips. The series recreates, in editorial form and content, the flavor of the paperback crime novels of the 1940s and '50s. The covers feature original illustrations done in a style that was common for paperbacks of that era, credited to artists such as Robert McGinnis and Glen Orbik.

From the Wikipedia article “Hard Case Crime”, licensed under CC BY-SA 4.0.

An imprint is a brand inside a larger publishing house, often with its own editors and list. Imprints of large groups usually acquire through literary agents; read recent titles to see whether your book fits the list, then target agents who sell to it.