Looks like the crew of this PV-1N "Eight Ball" chose to list a memorial for another crew who were lost on a previous mission.
Circumstances Of Loss:
Captain Duane Jenkins flew a PV-1 Ventura night fighter with VMF(N)-531. His crew – which included Staff Sergeant Charles H. Stout, Sr. (radar operator) and Sergeant Thomas J. Glennon (turret gunner) – were credited with scoring the squadron’s first kill when they splashed a “Betty” bomber on 13 November 1943.
Sergeant “Tommy” Glennon operated the turret guns aboard a PV-1 Ventura night fighter with VMF(N)-531.
Staff Sergeant Charles Stout operated the radar set aboard a PV-1 Ventura night fighter with VMF(N)-531.
On the night of 3 December 1943, Jenkins’ crew departed from Barakoma in PV-1(N) #29857 to patrol over a task group heading for Torokina, Bougainville. Japanese planes found the ships at 2000 hours, and the Ventura vectored in to intercept. The details of the fight were lost in the darkness, but played out on radar screens:
At 2211 a plane was seen shot down in flames by another plane seven miles east of the formation. The PV-1 night fighter was the only friendly plane in the area. Afterwards, the plane still flying showed friendly, and flew east for about one minute, where it was lost.
Dane Base at Torokina Point followed the night fighter chasing [a] bogey and saw the blips merge. Nothing further was heard from the PV-1, and the plane did not return to base.
War Diary, VMF(N)-531
Jenkins, Stout, and Glennon were officially credited with a second kill – but were never seen again. Exactly what caused their loss is not known.
No remains were ever found. All three Marines were reported missing after the mission, and officially declared dead as of 5 December 1944.
More information here:
https://missingmarines.com/duane-r-jenkins/
PV-1N Ventura, Bureau Number 29811, "Eight Ball." Photographed at Bougainville, 25 June 1944

Detail of 'Eight Ball' with nose art, painted-over windows, and crew memorial.

War Diary of VMF(N)-531, December 1943. Very poorly written IMO.