An experiment examined five signal words on safety signs for effectiveness at communicating information about severity of a hazard. Perceived severity was rated by 59 college students for the signal words Deadly, Danger, Warning, Caution, and Notice. Results indicated that Deadly communicated the highest ratings for severity. Danger was second. Warning and Caution were tied for third. The lowest ratings were for Notice.
Jensen, Roger C. and McCammack, Andrew M., "Communicating Severity of Hazard with the Signal Word on a Safety Sign" (2004). Safety Health & Industrial Hygiene. 10.