Due to recent increase in cat thieves, many local law enforcement are offering free etching of the catalytic converters. Some local businesses are also doing it for free or with a nominal charge. Check your local news for such free event from local law agencies. Some of my neighboring cities have these event this weekend.
It is not going to stop someone from cutting the cat off, but it make it more work for them to get money for them. They will need to grind the etching off, and some "honest" recyclers do not accepted cat with etching or grinding mark on them. The thief will need to cut the cat open and break up the honeycombed structure inside and sell it on ebay for much less money.
I am going to etch it myself with a etching tool if I can't find anyone doing it for me for free.
etching catalytic converter
etching catalytic converter
2000 Concourse dinette, on 1999 6.8L Ford E350 Triton V-10 Chassis