Along the bottom of a cheque is printed a number of funky space age looking numbers representing the account number, sort code and cheque number. In fact this is an early method of computer character recognition (dating back to the 1950s) which banks used to automatically sort cheques. The numbers are printed using ink loaded with iron oxide. When the cheque is passed through the reading machine, these numbers are magnetised. The numbers are then passed under a small electric coil, a voltage signal is induced by the magnetised characters [1]. The computer is programmed to recognise these signals and therefore can read the numbers and perform any relevant operations such as sorting cheques by sort code or account number. This process is known as Magnetic ink character recognition or MICR.
Obviously you need a special font for this, so that each magnetised character returns a different and unique signal. These fonts are known as MICR fonts and two are in general use worldwide. In the UK and US the font used (those space age numbers) is E13B. This font only includes the ten numerals and a few special characters, it does not have any alphanumeric characters. The other common MICR font CMC7 does include a full alphabet though is not read in quite the same way as E13B.
The full character set for E13B is shown below.
[1] Barry Wilkinson & David Horrocks, Computer Peripherals (2nd Edition) (Edward Arnold, 1987) p. 216
