The “I” you are looking at may be a number one.
The serial number on mine looks like its stamped, but on closer inspection it is actually engraved in VERY small writing, so small and neat that it looks like stamping, see: http://s133.photobucket.com/albums/q...ent=Serial.jpg
Someone did a survey on numbers here: http://www.airgunbbs.com/forums/show...NUMBERS&page=3
That may help you, I'm no expert but as there does not seem to be a GI there or or even a GH, could it be G ONE?
So is it basically a "G"?