Yes, that's a McGivern bead front sight.
The grip adapters were available in late 1931, but the patent for them was not formally granted until early 1932.
My OD from February 1932 (shipped about six weeks after yours) has an oversize McGivern bead now, but according to the letter left the factory with a Call gold bead; these were flush to the rear face of the sight, not domed above it. The gun also came to me with grip adapters mounted, but they were not referenced in the letter and must be a later addition.
I'm not sure when S&W began offering the McGivern gold bead as an option. Did your letter say your gun shipped with a Call or McGivern bead?