65 ILCS 5/3.1-55-5: Certificate of appointment.

Whenever a person has been appointed or elected to office, the mayor or president shall issue a certificate of appointment or election, under the corporate seal, to the municipal clerk. All officers elected or appointed under this Code, except the municipal clerk, alderperson, mayor, trustees, and president, shall be commissioned by warrant, under the corporate seal, signed by the municipal clerk and the mayor, acting mayor, or mayor pro tem, or presiding officer of the corporate authorities.