Like Brad said,
Spend the cash and replace that circuit's breaker with an arc fault, you'll protect all the outlets on the circuit without having to worry which are wired properly.
That sounds so cheap and easy when all you have to do is type it. 
Arc faults can be a big nuisance. They will usually trip when you plug anything in that has a spark inside. That would be any universal style motor. (anything with motor brushes) Vacuums, drills, saws, etc.
An arc fault breaker does not serve the same purpose as a gfci.
Also you can not put gfci breakers in the panel if the circuit is served by a 3 conductor cable. (one circuit on the black wire and one circuit on the red wire sharing a neutral. They will nuisance trip all the time or might not turn on at all.
Also if you fiddling around in the panel those types of circuits need to be on opposite phases. If not you expose that shared neutrual to the combined amperage of both circuits. 20+20=40. You will melt down the neutral and never trip the breaker.
Seen many of failures caused by this. Homeowner needs extra space for something, Rearranges breakers or puts in a tandem to make space. The neutral will usually burn off at the buss. (thin spot in the wire from being crushed to death under the screw)
