The most common Scotch kiss is a type of candy in which a marshmallow is coated with a butterscotch shell. 'Kiss' was a common term for a small candy in the early 1900s, and Scotch is simply a shortening of butterscotch. It is not a specific brand name, although See's is perhaps the most well known maker of Scotch kisses.
These days, a Scotch kiss is sometimes used to mean a headbutt, in which one person uses their head to hit another person's head, hopefully knocking them out. The phrase Glasgow kiss is currently the most common demonymic way to refer to a headbutt, but Liverpool kiss, Kirby kiss, and Swindon kiss are also kicking around.
And most oddly of all, the original meaning of Scotch kiss is the apparently previously perfectly normal practice of kissing someone while holding their nose.
"Scotch kiss, a kiss given while each kisser holds the other's nose between thumb and forefinger, and places the other hand under the chin."
A Vocabulary of the Anglo-Manx Dialect, by Sophia Morrison, 1924
While clarifying references to Scotch kisses are few and far between, it appears that this was most often done by children to their parents or other family members, as a way of saying hello or farewell. It is not at all clear if this was in anyway connected to Scotland, as 'Scotch' used to be a common adjective to add to something that was poor or foolish, much the same way as a Dutch kiss (variously meaning a loud kiss, a kiss on the forehead, a smack, or a kiss anywhere but the face) doesn't actually denote the customs of the Netherlands.
Unfortunately, this custom is now either extinct or, perhaps, goes by another name, and so we don't have clarification if this was simply a childish way of pulling someone in for a kiss, or if reciprocal nose-holding was a key part of the interaction.