I had mine done today. They used acid, painted on thru' a perforated tape. Almost invisible - tho' they did it on the crossbar, before I noticed, while I was filling out a form...which I wasn't too thrilled about. Not that it matters too much for me on my battered steed, but if I had something fancier I might be a bit peeved. You'd think they'd at least ask.
It probably won't make any difference, but on the other hand, it can't hurt and you never know. Why postcode when you've already got a serial number? 'Cos with your house number & postcode, they can trace it back to you. What use is a serial number, if they've nothing else to go on?