On rare occasions (for instance, on the publication of an eagerly awaited or controversial book), a publisher may require the recipients of an ARC to sign a confidentiality of content agreement.
[1] Before it was a common practice to produce and distribute ARCs in this way, publishers used uncorrected, bound galley proofs only for the editing and proof-reading process.
Typically, they were bound in plain paper covers without illustrations, printed in black and white, and significantly larger than their market book counterparts.
In contrast, ARCs usually are printed in full color, and have bindings, format, and illustrations that are similar to those of the market book.
Most advance copies have a printed-on label on the spine and possibly the front cover with the release year and month of the final book.