In the State of Washington, they compare the signatures on the petition to the voter rolls to see if the signature matches.
Here is an interesting link to the details of the petition on the referendum that actually triggered this Supreme Court case:
http://wei.secstate.wa.gov/osos/en/initiativesReferenda/Pages/R-71SignatureStats.aspx
You should take a look at the Produce Traceability Initiative (PTI). We are just getting into the first steps of implementing this where I work (a regional produce distributor). Much of the traceability is already there, BUT every company has their own system. Recalls are a major pain - this will completely solve the problems. PTI provides a universal barcode on every box that traces the produce in the box to the farm level and which specific day it was picked.
I don't have any use for bodyguards, but I do have a specific use for two highly trained certified public accountants. -- Elvis Presley
