See, CNN interviewed two folks for this story: The lady who took the photo and a UFO investigator named Cameron Pack. Pack points to a similar UFO that was photographed near Fort Belvoir (also in Virginia) back in 1957 as evidence that this new photo might be something spooky. More on that later. Mrs. Smith, for her part, disagrees with Mr. Pack and thinks instead that maybe this smoke ring was a sign from God Almighty. It's not immediately clear what that sign is meant to indicate, but I think this lady may get extra credulity points for immediately jumping to divine intervention as her first explanation for a weird-looking cloud.
One thing that is immediately clear, however, is this:

The towering monstrosity pictured above is Volcano, a roller coaster at King's Dominion that, among other things, is in the business of periodically launching gigantic rings of smoke into the air. I'm going to take a wild stab in the dark and posit that perhaps, just perhaps, the huge smoke ring in Mrs. Smith's photo might not have been produced by a vengeful deity but instead by the 155-foot tall smoke ring machine located nearby.
As for the 1957 Fort Belvoir photos, the incident was investigated by famous Condon Committee 50 years ago and was found to almost certainly be the result of an A-bomb simulation conducted at the Fort Belvoir military base. This simulation and others like it conducted at the base, according to a report from the Condon Committee, consisted of "[f]ive 55-gal. drums of gasoline, diesel fuel, TNT, and white phosphorus" that were arranged in a circle and then detonated. That certainly does seem like it could create a bit of a smoke ring. The report also noted signs that at least one of the photographs may have been retouched to make the smoke ring "appear more regular and more puzzling." The full report on the incident (as well as the full text of the entire Condon Report) can be viewed at the excellent website of the National Capital Area Skeptics.
So there you have it - Two "UFOs", fifty years apart, that looked mysteriously like huge, floating rings of smoke have been revealed to be...huge, floating rings of smoke.
Poof.