Numerology

You pick it up and read some:

"Numerology is the use of numbers in place of letters, and is often a code which can be manipulated easily to obscure messages in a uniform fashion.  While it is easily cracked, it can be harder if the letters and numbers are not in sequential order. 

It is necessary, as always, to decode the message as a whole instead of assuming that the code changes every word."

Shrugging, you put it back.  Time to go back out into the square.