"Yours" as closing

Two real problem origins for me, can someone help? I'm a librarian in Ohio, USA in a High School and cannot find an answer to either of these phrases.

Played like a fiddle-meaning to be manipulated artfully.

Yours truly-as in the sign off of a letter.

When/where did this begin in our language???

The Oxford English Dictionary's earliest example of "yours" in the closing of a letter is dated about 1430. There have been many variations.
"Yours to death, and after death, Luke Kirbie"
"I depend on your mighty Talent . . . and on that Score, remain, Most Lovingly Yours."
Presumably the early examples were written in England.

I couldn't find anything about the "fiddle" expression.