I don't remember what my No-Prize was for. It may have been something about the X-Men. The original X-Men, this was in 1968 or so. A year or so later I went into a deep depression and stopped reading comics for almost two years, and in that period I lost the No-Prize envelope.

I never tried and therefore never won, but IIRC, a no-prize was just that.

I made a quick visit to Wikipedia: en.wikipedia.org/wiki/Marvel_No-Prize

Predecessors and antecedents of the No-Prize
The No-Prize was inspired by the policies of many other comic book publishers of the early 1960s — namely, that if a fan found a continuity error in a comic and wrote a letter to the publisher of the comic,[2] he or she would receive a prize of cash, free comics, or even original artwork.[3]

In a similar vein, in 1962, Marvel Comics writer/editor Stan Lee promised, in the letters page of Fantastic Four #4, that he would send five dollars to a reader who would write in with the best explanation for a continuity error from an earlier issue.[4] When the Marvel offices were inundated with suggestions, Lee awarded the $5 to the first letter received, and printed the names of all the other correspondents who had sent in good answers.[5]

The first No-Prizes
This sort of interaction with the readers continued, with contests and polls being run on the Fantastic Four letters page for the next few years.[3] In the letters page for issue #22, featuring a contest for which reader had the largest comics collection, Lee announced that "no prizes" would be given ("because we're cheapskates!").[6] The winner of the contest was announced in issue #25, where it was officially dubbed a "No-Prize."[7]

In Fantastic Four #26, Lee ran a contest asking readers to send in their definition of what "the Marvel Age of Comics" really meant. As part of the letter, Lee wrote "there will be no prizes, and therefore, no losers".[8] Originally, the "prize" was simply Lee publishing the letter and informing the letter-writer that he or she had won a No-Prize, which was actually nothing.[9]

Other No-Prize contests asked readers questions and rewarded the most creative responses. One example asked readers for proof of whether the Sub-Mariner was a mutant or not.[citation needed] Winners had their letters printed, along with Lee congratulating them on winning a No-Prize.[3]

For "meritorious service"
The No-Prize had been intended as a reminder to Marvel readers to "lighten up" and read comics for pleasure; to not write in for prizes, but instead for the thrill of being recognized for their efforts.[3] Letters soon multiplied, however, as fans wrote in looking for errors in every comic they could, and suddenly the non-existent prize was in high demand. In response, Lee took on a new approach.[3] Since other comic companies had given out prizes for pointing out oversights and continuity errors in their books, Lee began awarding No-Prizes in such situations only "to the fan who could explain a seemingly unexplainable situation."[3] The reader who inspired this version of the No-Prize was a teenage George R. R. Martin, later a successful novelist.[10]

The No-Prize soon evolved into a reward to those who performed "meritorious service to the cause of Marveldom": readers who first spotted a mistake, or came up with a plausible way to explain a mistake others spotted, or made some great suggestion or performed a service for Marvel in general.[11][3]

No-Prize distribution
As time went by, some recipients of the "award" began to write Lee and ask why they had not received an actual prize.[3] In response, in 1967 Lee began mailing No-Prize-winners pre-printed empty envelopes[3][12] that said "Congratulations, this envelope contains a genuine Marvel Comics No-Prize which you have just won!" However, some uncomprehending fans wrote back asking where their prize was, even going so far as to suggest their prize had fallen out of the envelope.[3]

Confusion and decline
After Lee stepped down as Marvel editor-in-chief in 1972 (becoming Marvel's publisher),[3] Marvel's various editors, who were left in charge of dispensing No-Prizes, developed differing policies toward awarding them.[3] By 1986, these policies ranged from Ralph Macchio's practice of giving them away to anyone who wrote a letter asking for one to Mike Higgins' policy of not awarding them at all.

Welcome aboard. It's always nice to have another member with a Legion of Super-Heroes avatar.