Questions about Oregon initiative and referendum signature petitions are as old as the petition itself (1902) and as new as yesterday (see History links, below). The latest challenges are to the Secretary of State’s office tossing petition signatures for a 2010 ballot initiative that would change how the state manages legislative redistricting.
There are lots of recent news stories; online news readers can Google (or otherwise search) “oregon initiative petition signatures” with any variations you wish that develop as you read the stories. Don’t forget that the phrase “valid signature” may not be used in a story about petitioner signatures and instead, there may be words like signature verification, authentication, and similar words used in conjunction with the words petitions, signatures, and initiatives.
Keep in mind also that I know little about signature petitions (see Disclaimer, below), let alone the initiative and referendum process (other than as a voter), so come along on my: