If you spot anything while voting or helping out that seems out of place--anything--report it. The campaign and voter protection organizations can't help remedy problems unless there's a record of it, so do not hesitate to report an issue, no matter how minor you think it may be.
Obama Voter Protection:
Call 1-877-US-4-OBAMA (1-877-874-6226) and let them know what problems you're seeing. If you can't get through, use this online form and/or call your local campaign HQ.
You can also call Election Protection, a nonpartisan organization: