I think I have pictures of the same gun but whoever sent them blocked out the first two digits of the serial number on the straight grip trigger guard backstrap leaving only 900 showing. It must be a late gun in the 18xxx or 19xxx serial number range, as it doesn't have a rectangular extension of the barrel lug extending through the bottom of the frame, a feature into the 17xxx range --
15174 11.jpg
The single trigger on this gun appear to be the same as on Frank Tobin's personal gun, but is not the one shown in Tobin catalogues which has a round screwhead button which slides fore and aft ahead of the trigger as on this No. 55ET Model Grade --
No. 55ET Left.jpg