I have searched the ATF regs, this forum, and some other forums and can not find any place that indicates that it is REQUIRED to mark the barrel of a re-barreled rifle with the appropriate caliber.

I fully realize it is a good idea to do so, and is another step in keeping things safe.

My question is: Is it required by law or ATF regulation, and if so, can you help me find the appropriate citation?

If I have missed the answer somewhere in my search, or if this has already been addressed, a simple link to the answer will suffice.

Thanks for your help.
Happy Easter!