It's an apostrophe, not a comma, and unfortunately that won't work in the case where it should be "it's", like at the start of this sentence, but yes. "It's" only ever means "it is" or "it has". </pedantic>
Disregarding the semantic absurdity (and the e/i mismatch), the rule works fine: "his an apostrophe" should look a lot more wrong to anyone with enough understanding of English that its/it's mistakes make a difference than "he's an apostrophe".
"He's" also only ever means "he is" or "he has", just like "it's". That's the entire point of this little memory aid.
Disregarding the semantic absurdity (and the e/i mismatch), the rule works fine: "his an apostrophe" should look a lot more wrong to anyone with enough understanding of English that its/it's mistakes make a difference than "he's an apostrophe".
"He's" also only ever means "he is" or "he has", just like "it's". That's the entire point of this little memory aid.