To identify illustrations or art work by Gerald McConnell, take notes. Due to a large pool of artist producing paperback book covers in the late 50's and early 60's, the publishing houses got to set the rules to some extent. Artist starting out couldn't really set price, but the known artist could at least push for top dollar. To get known, your signature needed to be on the published work. The publishing houses, however, would tell you not to sign the art or they simply cropped it out, stating that you hadn't earned your position in the market, a nice little "catch 22" that benefited the publishing houses.
The majority of the unsigned work on this web site was attributed by Gerald McConnell prior to his death. On most of his book and magazine covers he would work in gouache and set one color for the entire background. Then when using white (for smoke or horse kicking dust for example) he would paint the white over the background color. This is usually a good item to look for when first trying to attribute his unsigned art. After that it requires a good understanding of his styles.
When coming across work that is signed, he had started out signing work "Mac," and used a signature for a very short while, but primarily printed his name in his notable style. He even signed his checks the same way. In the late 70's he added the copyright symbol as he continued to fight the big publishing houses that would pay for onetime use of artwork and then republish the work years later on different books without compensating the artist. He took many to small claims court and won every time.