Riveting Serial Number Plate

[mud99]

I am building an 80% AR Lower.

I know that I do not need to have any markings on it at all, however, I would like to put on a serial number in case I one day want to sell it.

Is it acceptable to rivet a plate to the receiver with the serial number? How permanent does it need to be?

Alternatively, can I solder the plate on?

As to the serial number itself, I was thinking of milling small dots and dashes, and putting it in mourse code. Does the serial number need to be in roman characters?

[Grumpyoldretiredcop]

You will find the answers to your questions here, right in the first section. Be aware that you are only required to mark your receiver in conformance with the Federal code linked here if you desire to sell or transfer it sometime in the future. I don't have an opinion about marking your receiver in Morse code... that could be interesting given the print size requirement.