On Sat, 14 Apr 2012 16:32:01 -0700, Steve B wrote:

Supposing a guy wanted to put a hidden identifier in a product.

How well hidden? We are marking our aluminum sample holders with laser-
burned QR 2D barcodes (check google if you don't know what I'm talking
about). They can be quite compact: a 5mm x 5mm symbol can fit a dozen or
so characters.