Stop sign, Speed Limit sign, No passing sign, Railroad crossing sign and yield sign are the most common ones on the signs test
Hint: If you ever need to take the drivers license/permit test, take a look at this site:
http://stevefrey.com/2010/07/30/nort...t-study-guide/
When I moved to NC and had to get an NC license, I read over that site and 90% of the questions on the exam were verbatim off of that list. The examiner was shocked at how quickly I completed it