In that era, Iver Johnson advertised its "hammer the hammer" (transfer bar system) and H&R had nothing comparable. So they simply removed the spur from the hammer (making it harder for the hammer to be accidentally driven into a cartridge primer if the gun was dropped), called it a "safety hammer" and pretended it was as good as IJ's transfer bar.
H&R and IJ revolvers of that era are gaining respectability with collectors, though they still are not high value and (due to the huge number made) are of collector interest only if in top condition, which very few are. Geneally value runs under $100, but yours should have more value to you because of its history.
IIRC, H&R did not serial number those guns, so the number is probably a batch or assembly number.