Located on inside-front cover
He's called simply 'Lightning' throughout the story, except in the opening and closing captions.
In addition to the signature on splash page, Jim Mooney signed in two other locations within the story. Once within the last panel on page 6 of the story, and again in the 4th panel on page 11 of the story. Both additional signatures are written as just "Mooney".
The final panel includes a request from the publisher for readers to write in and let them know if they want more Rx Dr Nemesis stories to appear within Lightning Comics.
A previous indexer has noted that the story was signed by the artist (Harry Anderson), however I was unable to locate a signature on a scanned copy I read on Comicbookplus.
Jack Alderman's signature appears within the last panel of the story, the panel serves as a promo for Hap Hazard's appearance in the next issue of Lightning Comics.