Don't submit in any tone, as this looks like it was toned to a sepia image. Don't include signatures.
Personally, I don't think the aesthetics are very good. It kind of looks out of proportion. As it is, it wouldn't sell.
The drawing isn't very flattering!
Read this to start off with:
Since we don't know the reason Adobe gave for rejecting your image, it's hard to comment.
Stock images must appeal to a wide range of content creators who need images for use in their own projects -- videos, product packaging, commercials, websites, t-shirts, etc... Stock customers expect technically & visually perfect full color images. Vector graphics are usually preferred for drawings because vectors can be rescaled to ANY size without loss in quality. You can't do that with raster images (JPG).
See links below.
Looks more like a "fine art" illustration. Probably better suited for that. But lets not throw out the baby with the bath water. You can always make a simpler line drawing or similar with a vector creation program. Best bet, use Illustrator. If you can't afford that program right away, you can always make this into a JPG or use a look alike vector program till you save a bit of money for Illustrator.
Just my oppinioon. 🙂