One article I read made the case the "reasonable suspicion" is in a family of terms including "preponderance of the evidence." A preponderance of the evidence seems to me to be require a better than 50% likelihood. That's why it was so easy for the civil jury to find O. J. liable for the double murders, even though he was acquitted in criminal court. Civil court requires a preponderance of the evidence, criminal court requires that it be beyond reasonable doubt. It seems to me that one way of construing SB 1070 so as to avoid some of the most serious concerns about it would be to construe "reasonable suspicion" in just this way. While most illegals in Arizona are Hispanic, most Hispanics in Arizona are not illegal, and therefore merely being Hispanic should not be sufficient to generate reasonable suspicion so defined. Even criteria like lower-class clothing, playing Spanish-language music, and communicating mostly in Spanish would not be sufficient for reasonable suspicion. Though I suppose standing on the sidewalk of a Home Depot looking for day-labor work might be sufficient.
The point is, if a person is asked for papers, there has to be sufficient objective evidence that makes it more than 50% likely that the person is here illegally. (I admit that being a subjectivist about prior probabilities makes this recommendation more difficult.)
I kind of doubt I'd vote for the bill if I were a member of the State Senate even with this gloss. But it would certainly help if it were understood in this way.