The grips on Captain Sparks’ pistol are known as “Sweetheart grips”
and were common during the war. Soldiers made them from the Perspex
windows of shot down aircraft specifically to put pictures of their
sweethearts under as a good luck charm. This also explains why in the TV
series Felix was desperately trying to reach for his pistol when got
wounded.
According to Alex Kershaw’s book “The Liberator”: “In one
village [Felix] found a craftsman, who replaced the pistol’s standard
grips with transparent plastic taken from a downed American bomber’s
windshield. Sparks set a photograph of his son, Kirk, and wife, Mary,
under one grip and a favorite pinup under the other”.
Alex Kershaw’s book could be purchased in various options (hardcover, paperback, Kindle, audiobook) on Amazon.