I have always thought that your legal signature had to be "the same" each time. Not that you can absolutely replicate the strokes, but if you habitually use a middle initial, then if you sign without the middle initial it's not your legal signature.
For example, my father's first name was the same as mine, but he didn't have a middle name. I do -- so from an age so young that I can't remember, I have always used the middle initial to distinguish me from my father. By the time he died, it was second nature so I continue to use the middle initial version as my legal name, and my signature. Exceptions are when cashing or depositing checks that don't include the middle initial, or that include the middle name rather than the initial. Checks get endorsed as the payee appears on the face, or the bank teller comes unglued.
On my mother's side, four consecutive generations had the same name, so their signatures included "Sr.", "Jr.", "III", or "IV." My uncle hated the fact that he was "IV," and I noticed that very soon after the death of my grandfather he stopped using the Roman numeral. I have always regarded that as a sign of disrespect.
