(a) A deputy clerk may execute all documents required by law to be executed by the municipal clerk and may affix the seal of the clerk wherever required. In signing any document, a deputy clerk shall sign the name of the clerk followed with the word “By” and the deputy clerk’s own name and the words “Deputy Clerk”.
     (b) Except in municipalities with a population of 500,000 or more, the powers and duties of a deputy clerk shall be exercised only in the absence of the clerk from the place where the clerk’s office is maintained, and only when either written direction has been given by the clerk to that deputy to exercise a power or the corporate authorities have determined by resolution that the municipal clerk is temporarily or permanently incapacitated to perform that function. In municipalities with a population of 500,000 or more, the powers and duties of a deputy clerk shall be exercised upon the direction of the clerk, or when the corporate authorities have determined by resolution that the clerk is temporarily or permanently incapacitated to perform those functions and duties. When a deputy’s signature is duly authorized as provided in this Section and is affixed by a deputy in the manner prescribed in this Section on any document (including but not limited to contracts, bonds, or other obligations of the municipality), the document shall have the same effect as if the document had been signed by the municipal clerk in person.