I don’t know you’re exact position, but don't forget to let the letter check by the management/boss/commander/mayor. It can be political sensitive. For smooth and effective operation, we need the politicians to trust and like us (“we” don’t need politicians to tell us what to do in an emergency) . So keep them happy to a certain extend is vital.

When signing the letters, let a person sign who is in a political neutral position, by the public conceived as knowledgeable and reliable. It helps with the “trust” issues for citizens.

As for the letter. I’m not sure how much work you are planning to invest. Be aware that it is a relative ineffective tool to change human behavior. I do expect it to be more effective than campaigns by the government, because it’s more local and it’s address to people personally.

You might consider a separate letter or extra attention for citizens who have had a lot of luck during previous emergency’s. “Unrealistic optimism” is a common issue with people who where unaffected by previous emergency
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