The crosshairs are usually registration marks. Nearly every multi-color printed item has them on the paper before trimming to final size. Plus a lot of other marks.
The ones on the T206 proofs seem to me to be more layout oriented. In other words, marks used to make sure the location of the corresponding colors were exactly lined up on the stone. Once the stone was considered finished, they'd be erased from the stone.
To me proofs are fascinating. They show a portion of the entire process for making the final product. Some places do a lot of proofing. Topps has a vast array of different sorts of proofs. Some for the design pahse, some for the production phase. A lot of the final lining up Bridwell mentioned is done on the press with the regular production plates or stones. The sheets produced can be either nearly perfect or truly horrible. The shop I worked for usually had it near perfect first time, and perfect in less than 10 sheets. They also did nearly no proofing, any that I saw were photographic developed from the final sheet of negatives.
Not prewar, but here's one that crosses that proof/regular card boundary.
This is from the corner of what's called a "make ready" sheet. The magenta is printed a bit low. At the lower right are a couple lines that are registration marks. They should be printed right on top of each other. The torn top right corner is the special part. In order to keep the make ready sheets separated from the ones that will become releaseable product we used to tear off a corner of one sheet as a marker. Apparently Topps did the same thing. You can see the blue of the batting helmet printed onto the torn surface. It's not bleed through, as the card is printed on a surfaced board stock. The surfacing prevents the ink from soaking in, which keeps the image crisp.
So it's a production card, on the production material, printed from the same plates. But it's also partly a proof, since it was used to test the press adjustment. (Plus it's got the wrong back, printed lower than the front)
I'd like to think they went back and did a bit more adjusting. The shop I worked for would have considered this unacceptable registration. But I've seen enough 82 Topps to know better.
Steve B