On the face of it, dealing with the words themselves means this check is no good and you'll have to find the maker to determine why it's no good. In banking language, however, it means this check is 99% sure to be a fraud, but the bank can't say so. NSF on the check can be disproven if the records show a good balance - but the officer knows the balance is false, and fraudulently inflated. So I can't put NSF on it. The signature agrees. "Funds subject to hold" means I better have some documentation to back me up. However, I may be taking action on nothing but a phone call And I'm in even more trouble if I put "suspected fraud" on the face of the check. So the catch-all - used by almost all financial institutions (particularly the very large ones) is "Refer to Maker".
If you can't find a good, standard reason to put on the check as the reason for return, and the reason you are returning it puts even more liability on the bank, then "Refer to Maker" is your answer.
