Neither Mark Kilby Stands Alone nor Mark Kilby and the Miami Mob includes a formal credit for the cover artist. The art for Mark Kilby and the Miami Mob, however, is signed “Abbett” — short for Robert K. Abbett — in the shadow cast on the ground by the reclining blonde woman in the straw hat:
[CLICK IMAGES TO ENLARGE]
ABOVE: Robert Caine Frazer, Mark Kilby and the Miami Mob (New York: Pocket Books, 1960), with cover art by Robert K. Abbett.
ABOVE: Robert Caine Frazer, Mark Kilby Stands Alone (New York: Pocket Books, 1960).
As usual, both of the above covers were scanned by me from crumbling old paperbacks in my personal collection.