Not Ino, GR2. It’s Jno. The J is the same as in John.
I don’t know why Jno was an abbreviation for John, but I know it was.
I wrote Ino rather than Jno because that's how it appears in the two signatures. You tend to see the J in Jno written without a tail, as here. When he signs his name John in full, he does give the initial letter a tail.
The ultimate origin of the abbreviation Ino/Jno is the Latin for John which can be written Iohannes or, in later texts, Johannes.