In the past, when people wrote letters by hand (with a pen) or on a typewriter, they used to sign the letter 'justified right' (on the right side of the page).

But nowadays, the signature can be left or right justified (left side or right side).

Usually emails are always aligned with the left margin.

Here is a good website that explains the format of letters:

http://www.idiotsguides.com/business-and-law/general-business/business-101-writing-formal-business-letter/

Bottom right.   I worked for a few lawyers, before I found my feet and went into social work and it was how it was done.

Some people write  :   Respecifully yours, Sincerely yours, Yours sincerely, Very truly yours, ...

(I'm a U.S. native speaker)

I've always centered the complimentary close ("Very sincerely yours,") my signature, and my printed name.

Of course, I learned that in typing class in the 1960s and I haven't checked so I could just plain be out of date. It seems odd that we would have been careful to center them back in the days before word processors--yep, you counted the number of letters, including spaces, divided by two, and hit the backspace key that many time--and not now.