680 IAC 2-3-15 states that certificates shall be posted under glass in the room containing the equipment. It also states that; in the case of outdoor or portable equipment the certificate shall be kept in a metal container fastened to the equipment, or kept indoors in a place convenient to the equipment.
Note: It is recommended that owners provide a photocopy of certificates where the environment is not conducive to posting of the original certificate and maintain the original certificate in a safe environment. In any case, the certificate must be readily available to any official requiring proof of its issuance. http://www.in.gov/legislative/iac/iac_title?iact=680&iaca=2