Bill Goforth should be along and can answer your question. On my Dad's old IJ Safety Hammer Model the serial stamped on the trigger guard is 86XXX and Bill told me (if I remember correctly) it was made in 1921. This would place yours earlier. But that's just a WA guess.
in order to properly identify any iver johnson's arms and cycle works 'safety automatic revolver' two things are needed 1. the complete markings found on the top of the barrel rib, any markings on the left side of the barrel and any markings on the bottom of the butt. 2.serial number found n the left side of the grip frame, this is where 99% of the letter codes are found. only the second year production of the first model (1895) will have a serial number and letter code on the bottom of the butt. also it help to know the type of hammer spring (flat leaf or coil). the attached image is an illustration from my book that shows where to look for any and all marking found on the safety automatic revolver. the number 6 location is where serial numbers and letter code will be found sratting in 1897
jgreene, thanks for the additional information but with out the serial number and letter code found on the left side of the grip frame, number 6 in the illustration(remove grips to see). the only additional information i can give you is the single patent date aug.25.96 was used between 1911 and 1913. this is within the third model era (1909-1941).
i have no information on purchases by michigan state police but the purchase of iver johnson revolvers by small police depts is documented.
trigger guard serial number are not dependable as the correct serial number (trigger guards are interchangable within a given model and are often found to be replacements. bill