It is an Fractur „I“ from Haubtlaboratorium Ingolstadt.
The S does not mean brass but “this is a case for the S bullet”. When copper content in brass was reduced from 72 to 67 percent (in German: Messing 67, Ms 67) as an emergency measure, the 67 was appended to the case type S.
Thank you both for corrections. i assume copper content reduction was a war shortage measure, when did it happen, which year? I got lost in Kent. If anyone remembers page number, I’ll greatly appreciate that.