no it's not a signal std it's a printer command std
so an adapter would not work unless an adaptor for each printer type was made
I have an samsung wifi printer which don't support airprint but I just got the free samsung printing app from app store and then it works (only when printing from inside the printing app of cause)
maybe one could connect the usb printer to an thing like the airport express which let you connect usb printers and print to them over wifi and then using a sony printing app
There are a number of of hardware solutions, but fairly expensive (probably cheaper to buy a new printer that supports Airprint) e.g.
But there are numerous software options, all of which will allow you to wirelessly print via another device on your network PC (Mac OS, Windows, Linux,....) or existing NAS (GoFlex, Synology,...) e.g.