Any sign required by section 3 of this act to be posted in retail mercantile establishments shall state whether or not it is a policy of such establishment to give refunds and, if so, under what conditions, including, but not limited to, whether a refund will be given:
a. On merchandise which has been advertised as "sale" merchandise or marked "as is" ;
b. On merchandise for which no proof of purchase exists;
c. At any time or not beyond a point in time specified; or
d. In cash, or as credit or store credit only.