This is an extract from The Philosophy of Language by A.P. Martinich, page 3
For the most part, words are used in such a way that the word
itself is not the primary object of interest [...] philosophers sometimes use single quotation marks to indicate that a word or phrase is being mentioned [...] 'Cicero' is a word with six letters.
Cicero is a word with six letters, might also work. 'Cicero' or Cicero is then used to mention the word itself.
Cicero is a word with six letters, implies that Cicero the person and not the word 'Cicero' is a word of six letters. So one can say that a word is mentioned if it talks about itself. And is not mentioned if it does not talk about itself. But a word is always used. The sentence "I like Heroin " do not talk about the word 'Heroin', but about the song by the Velvet Underground. Because you told us you used it to talk about the Velvet Underground.
I like Cicero and I like 'Cicero' mean different things, by the convention already stated. "I like Cicero" would imply, that I like the person Cicero, and "I like 'Cicero'" would imply I like the word 'Cicero'.