Aurora and FM had an ongoing relationship for many years and during the mid '60s this coupon could be found in the boxes of their monster models. It offered a free copy (i.e., random back issue) of FM if you sent in the coupon with 25¢ for shipping. Probably not a lot of these have survived, as they would have been used. These coupons have also been found in the SPP monster wallets.
From the Richard Olson collection.