Can a property owner use a posted warning sign to avoid liability for an injury in Ontario?

A warning sign can genuinely help, but it is not an automatic, guaranteed shield from liability. The Occupiers' Liability Act allows an occupier to restrict, modify, or exclude their duty toward visitors by giving adequate notice of a risk, and a clear, visible, and specific warning can go a long way toward showing the occupier took reasonable care and gave visitors a fair opportunity to avoid a known hazard.

Courts, however, look closely at whether the sign was actually adequate for the specific risk involved - a vague, poorly worded, or poorly placed sign may not be enough, particularly for a serious or hidden danger that a visitor would not otherwise expect. A warning also generally cannot substitute for an occupier also taking reasonable steps to fix a hazard that could easily and cheaply be corrected instead of merely flagged. Whether a specific sign was legally sufficient in the circumstances is a fact-specific question that depends on the wording, placement, visibility, and nature of the danger, not an automatic defence simply because something was posted somewhere on the property.