A quotation can be introduced with a signaling phrase and a comma or a complete sentence followed by a

colon

Explanation:

Quotations reproduce the original words from text or speech that the author or speaker made. In that respect, they can be introduced with an introductory sentence and colon. For example:

In his most famous monologue, Prince Hamlet contemplates taking his own life: "To be, or not to be--that is the question: / Whether 'tis nobler in the mind to suffer / The slings and arrows of outrageous fortune / Or to take arms against a sea of troubles / And by opposing end them."

Besides, quotations can be introduced with an introductory phrase and a comma, and by embedding the quote within a text without any additional commas or colons.