I read this phrase on the top of the cover of a book:
an I Can Read Book
I wonder whether "I Can Read" can be used as an adjective without a hyphen.
"I Can Read" is the name of the series of books. No hyphen is necessary, though quotation marks or some different font styling to separate "I Can Read" from the rest of the sentence would be useful. Without punctuation and all in the same font, and capitalized as you write it, it might be a bit confusing:
an I Can Read Book!
But if you change up the styling or punctuation (or even the capitalization) you're all set:
an I Can Read book!
Since an is lowercase I think it makes more sense for book to be as well. Plus this adds more separation between "I Can Read" and "book". But so long as there is some visual marker to distinguish "I Can Read" as the category of book instead of a logical part of the sentence, it should be fine. You definitely wouldn't use a hyphen, as "I Can Read" (no hyphens) is the name of the type of book.