Do Form 1 Engravings NEED to be in Metal?

So come January I am hoping to submit a Form 1 to 3D print a suppressor in PLA+. This suppressor is essentially going to be "disposable" in the sense that if experiences a catastrophic failure after a few mags I just destroy it, send the ATF a letter letting them know, it was free, whatever. I am aware that they sell metal engraved plates online that you can solder into the suppressors, however since the item is essentially "disposable" I would rather spare the cost of one if possible. I have a cheap engraving pen I got from harbor freight I use on my tools, could I just engrave the serial number directly on the PLA and be good to go?