Signature on ID card is a routine function which can be delegated to Manager HR or asst manager.
Why should MD spend his time in routine signatures.
HR can make list of employees,get photos,identifying marks etc and make suitable ID card,
depends on the management , they can assign any person who is responsible to look in routine work, or they can sign it by themselves, there is no such bar,
however if they assign anybody to sign the documents they have to send undertaking to concerned govt department of such person details, so that the govt officials do recognize the signature otherwise they may refuse to accept