R.I. Gen. Laws § 31-13-5: Signs prerequisite to enforcement of provisions.

No provision of chapters 12 — 27 of this title for which signs are required shall be enforced against an alleged violator if, at the time and place of the alleged violation, an official sign is not in proper position and sufficiently legible to be seen by an ordinarily observant person. Whenever a particular section does not state that signs are required, the section shall be effective even though no signs are erected or in place.