According to Michael Roennevig for the Houston Chronicle, a letter of good conduct is usually a personalized note, provided by a person's local police department or other government office, verifying that he is an upstanding citizen without a criminal record. These letters are most often requested when a person applies for work in a foreign country and a potential employer has asked for proof of the applicant's good character.
Roennevig explains that companies can encounter difficulties when they attempt to run a background check on a potential employee who has spent most of his time working on foreign soil. For example, a company in Malaysia who is considering hiring a U.S. citizen for an open position would only be able to investigate that applicant's criminal background in Malaysia. The person may show a clean record domestically but could have multiple offenses in the United States. Most foreign governments are unable to access the United States' criminal database. It isn't uncommon for foreign employers to ask a job applicant for proof from a police department in the United States to demonstrate that the applicant's criminal history is clean. Roennevig also recommends sending a written request to the Federal Bureau of Investigation for federal proof that no serious crimes have been committed while on U.S. soil.