> these techy things with some sort of code attached

I'm a techie, so (surprise) I took a close look:* the dots differed slightly from stamp to stamp in the same book. Either they're serial numbers, or they say whether they're first or second class citizens, or possibly both; either way, they're for the machines to read, not us poor human beans. At least those strangely-shaped numbers along the bottom edge of cheques were intended to be human-compatible as well as machine-readable.

* I can't scan them: I'm not a camera phone.