Detective Steve Bergren wrote to the Tarpon Springs Police chief that he was only joking when he made the remarks last month to a colleague.
The Tampa Bay Times reports that Bregren resigned last Thursday before Police Chief Robert Kochen could fire him.
In his letter to the chief, he apologized for his behavior.
Tarpon Springs Police Maj. Jeffrey Young says law enforcement can't ask the public to watch out for signs of potentially dangerous behavior and ignore such a sign under its own roof.
An internal investigation will be sent to state officials, which could affect Bergren's officer certification.
Information from: Tampa Bay Times (St. Petersburg, Fla.), http://www.tampabay.com.
Copyright 2019 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.