I Ayvazovski dozens of paintings signed on the reverse side of the canvas, cardboard ....

Canvas or stretcher is sobstvennst and mark her signature, is one thing.
A signature on the painting itself - this is to show the authorship of his work
Yes, or when give Canvas tighten on a frame. But is it necessary then this stretcher uses exactly the one who wrote his initials?
  Why, then, are the same I. Aivazovsky, Repin, so any author - signed on the painting itself?
  ... Well have at it some 10 thousand pictures and can be a dozen or so of getting caught,
A stretcher, canvas, so as not to be confused and not rested, clear
  But please explain, why does he own his work behind podisat decided?
And the show, please, if there is a photo

You reason like a boy, sorry.
First, the canvas is stretched DO that as it paints a picture.
Secondly, as a rule, the artist himself stretches, and before it selects a canvas, I mean the structure of the canvas - its density. To make it clear bag of potatoes from the "coarse" sackcloth, canvas for painting - from the more "shallow".
Third, what is the point to take someone else stretcher? To the neighbors think badly of you?
Fourth, but for what you name? You do this like other people, as you distinguish?
If practical, the artist signed on the front side to curious spectators did not touch the picture on the wall, peering from behind who wrote it. : p:)

The picture was signed by the artist because he painted it to be signed, like any author.
  The works are usually signed, painting, sculpture, theorem, poem, etc. Or do without a signature.
  A stretcher and canvas, as I understand it, before writing signed by the picture, or there is evidence of life, such as Aivazovsky,
  that - by writing "A ship in the bay .." Ivan Konstantinych unrolled the canvas and signed on a stretcher ..?
  Why Levitan on a tiny sketch in the corner scratch out his signature? not wrote in a big way at the back of the cardboard?
  By signing, what they have created, rather than something from what he is going to create. These things are simply marked signature.
  On the stretcher can be written by anyone, and the author as well. Is not it?
But the picture of the author only, and no one else. Because this is so? (not talking about fakes).

Dear, help where they can apply in order to get at least some information?

There are places where they can set the time of writing, pictures, and to confirm or refute the alleged author. But these services can cost equal to the painting itself. I think if you give good, high-resolution photos, pictures, and its fragments. And here you could say much more.
  I think that the most important thing to see the quality of painting. If highly artistic painting, it makes sense to bother the definition of the author.
  From a distance - the sky and water - clean Aivazovsky. Close yet seen.

I put a picture of another picture, look пожайлуста a new topic estimated that an additional one picture

A stretcher can be elementarily signed in carpentry. Since orders can be many, stretchers are made in a heap and signed by the worker. Then the artist comes and he shall issue an order by surname.
Canvases are signed back mainly on those works that are sent to the exhibition. It is easier to understand, what-where-someone. And the paperwork is less. Naturally, Levitan no point was not to sign the little sketches in the back, because he never planned to send them.

annacz, unfortunately for the photo that you sent could not understand anything.
I think that you should remove the picture from the frame and carefully examine the bottom edge.
It often happens that the signature of the artist hidden behind the projections of the frame and not visible to the viewer.

According to the plot (Crimea?) And the manner of painting was written much earlier than the date of purchase. Then, among the artists was not accepted to sign anywhere. And buyers, too, appreciated the signature on the painting. But, perhaps, the picture was much "поновлена" before selling, lacquer and recording potershihsya edges and unobtrusive signature disappeared, we need an X-ray ... Or is it a copy, then the absence of a signature on the well-preserved picture is more clear ... This is the case when the attribution requires this "museum" of knowledge, ie professionals, through whose hands and eyes is a lot of painting ... a certain period