Roll marks/stamps/etc

So this may be a stupid question but how do people get those custom rollmarks or stamping on their lowers?

Do you just call a manufacturer and ask for a blank and then send it off to someone to engrave?

Along the same lines...

The folks with FA settings/markings on their lowers... are all lowers the same (rated for FA fire/trigger assemblies)?

I have seen a couple with the FA, Spikes is one I believe. As far as other engravings etc if you look on gunbroker a lot of the companys will engrave stuff when you buy a lower. I think RAR guns can have it done also? One of these days I want to get an engraving done.