It's the current user at the moment of making latest changes to the macro. The hash is there for the integrity purposes - to make sure that the user who is signed in the macro is the one who makes the changes. That way it's ensured that you are not able to create a macro with the signature of someone else (the hash would't match). If it wasn't there, you as an editor could create a macro signed by a global administrator and get access to data you are not supposed to read.
I'd recommend reading Working with macro signatures.
Btw, you can always go to Macro Debug to see who signed the macro.