I'm very interested whoever will offer this marking service because I would not want to have to destroy my hardwork. Would like to find out ASAP because I imagine the few people that will offer this will end up having a lot of demand and a long lead time or wait list. And time is counting down.Well, yes, it does seem unfair for the state to make you into a criminal for having purchased something that at the time you bought it was legal to buy and have. They are allowed to do things like that, and it extends to many kinds of products, not just firearms, but things in common trade, like gold. What you miss in your example is that while buying and possessing the unmarked firearm was legal, continuing to possess it after a fixed date is illegal unless you bring it into compliance by means the law prescribes. Of course if the prescribed means are unavailable except to destroy the firearm and forfeit its value, the state has effectively taken it from you without just compensation.
To the other poster lamenting the fact that this thread is not confined to a list of FFLs providing marking services, I can say that some of us posting are actively exploring constructive options to accomplish just that, and that as soon as more progress is made, information will be shared here.