Norm,
It is not at all unusual for a pre-1916 Imperial Luger to retain its original alter Arte (old-style) sear bar. The rear toggle pin is properly unnumbered and unproofed; the requirement to serial number the part was issued in 1932. Also, the odd blue color is due to the "fire bluing" heat treatment of these parts, and is an indicator of the gun's having its original finish. The sear bar spring, front sight, and grip screws are fire-blued as well, although the finish is not durable and is usually found worn away from the sight and screws.
--Dwight
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