The only thing that concerns me is that usually Madonna signs her name in one consistent line. But this signature she stops on the 'd' and starts again with the 'on a'.
I 've never seen her sign one like this before. There are a few positives- I like the "onna" , especially like the "a" at the end. She's known for sometimes skipping one of the " n's" so it looks like "Madona, and that is done here. Both the "o" in " love" and "Madonna" have the centers filled in, which she normally only does in "love."
There are two stops that I've never seen and the v and e in love are strange.
Oddly, though, when I sit back and look at it, the slant is right and it looks good.
I'm on my mobile and cant read the verbage of the letter- is the document from early in her career? I'm seeing the Sire record label so it probably is....I'm leaning authentic but I'd want to see it on my monitor which I don't have access to. Let me take a fresh look tomorrow morning at a large image on something other than my phone.
It looks a lot like one my friend received through the mail awhile back.The O looks almost spot on as with the angle when compared so I would say its probably good.