I tried the marker route but found the ink fades after a short time here in the desert heat.
2 whacks of a 1.5# hammer on my HF steel stamps and the ingots are permanently marked until I melt them down.
I do use a tinted lacquer (from my antique finishing hobby) to spray the ends of the ingots by type for easy visual recognition. That stuff lasts a long time also.
I used to write the weight in oz on each ingot with a marker but do not waste my time anymore. Too many of the darned things and they are all around the same weight for the alloy they are made of.
bangerjim
ps How about RF? RF = roof flashing lead
Or XL = x-ray shielding lead
Or RL = range lead
2 letters (taped together with black electrical tape) are extremely easy to stamp with just 1 or 2 good whacks.
The combinations are only limited by your imagination. Just as long as YOU remember what the blasted letters stand for!!!!!!