I'd say it is just an earlier style checkering pattern before the trap forearm checkering patterns were formalized. Here is the listing from the 1922 Parker Bros. catalog which shows a DH-/DHE-Grade and the checkering pattern isn't what we later think of as the D pattern.
Trap Model Fore-ends 1922 catalog.jpeg
The Brothers P continued to use the same picture in their pocket catalogs for at least another eight years.