Please help us to define and evaluate the author's picture

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Сообщение от Eugene

Very often, especially in the 19 century .. And in the middle of 20 century in every second scene is a signature on a stretcher, or on the reverse side of the canvas.

Yes, it happens, but then the owner said, that the inscription on the frame.
  Interestingly, Levitan, Repin, Aivazovsky and so on. - See their signature on paintings. Clearly it painted and signed.
  And why is the sign frame or canvas with a turnover?
Can you explain?