The "Melts in Your Mouth, Not in Your Hand" slogan for M&M's began in 1954.
Interestingly in the UK that slogan ("Melts in the mouth not the hand") was applied to milk chocolate Minstrels - they were a large globule of chocolate covered in a sugary coating that had a melting point higher than 36oC (normal body temperature) and so didn't melt, whereas chocolate as a melting point a little under 36oC and so does melt, in the hand. I presume the m and m slogan is for a similar reason.
They were made for the troops in WW2 food packs. They came in small cylindrical tubes. It wasn't until 1954 the slogan was added, but the candy site doesn't tell why it was added.
m&m's
The slogan "Melts in your mouth, not in your hand" was used for M&M's to emphasize their chocolate shell coating that prevented them from melting in your hand. This slogan aimed to highlight the durability of M&M's and differentiate them from other chocolate candies.
McNuggetz
1954
They have many, some are "you can't resist M and they know it" and "always fun".
Melts in your mouth, not in your hands! This got across the message that because of the outer shell covering the chocolate, M&M's could be eaten even in hot weather without turning into a melted chocolate mess like a regular candy bar.
It melts in your mouth not in your hand. M&M
"Where's the beef?" was a slogan used by the Wendy's fast food company on TV ads in 1984."Melts in your mouth..." but not in your hands, was an ad slogan used by M&M Mars for M&M candies almost from their origin, 1941.
That was the advertising slogan for "Treats" the candy that melts in you mouth but not in your hands.ANSWER:That was the original advertising slogan for M & M's, "the candy that melts in you mouth but not in your hands".