The "smoking boots" effect is a classic standby of cheesy sci-fi movies, comics, and comparable media. It goes something like this:
([UNIFORMED HENCHMAN #50338] is escorted into the inner sanctum of the [ARCH-VILLAIN].)
Arch-Villain: Identification?
Hench: Number 50338, sir!
Arch-Villain: Assignment?
Hench: I was to follow Captain Perfect and ascertain what information I could, sir!
Arch-Villain: And what have you discovered?
Hench: Nothing, sir! Captain Perfect noticed me sitting on a tree branch outside his penthouse and
called the police, sir! I had to flee!
Arch-Villain: FOOL! IMBECILE! YOU HAVE FAILED ME FOR THE LAST TIME!
Hench: But, sir!
Arch-Villain: (turns to [IMPORTANT EVIL HEAD OF EVIL COUNTRY] sitting next to him) Ah, Mr. Prxxzt!
Would you care to see a demonstration of the Omega Death Beam 9000?
Prxxzt: Ah, yes honorable sir, by the beard of the Prophet, it does honor to my ancestors and my
crazy pantheon of voodoo gods to say that I would.
Arch-Villain: Good! Number 54, arm the Omega Death Beam 9000!
(Rumbling sounds are heard.)
ZAP!
…and all that's left of the henchman is a pair of smoking boots.
This is a classic effect in underrealistic books and film. I'm sure I've seen dozens of B-rated movies and campy children's shows where this happens, and you probably have, too.
Apparently the idea of this is to show off the fantastic power of whatever weapon, magic, or superpower caused the obliteration of the nameless henchman, without alienating us from his basic humanity. A wisp of smoke rising from the ground doesn't evoke much emotion, but a pair of boots — ah! That's humanity. You can almost see the henchman sitting up nights and polishing them, hoping that with diligent work he can be promoted to a Junior Assistant Patrol Officer, Third Class, or whatever. Also of note is the fact that this the departed was almost always wearing boots, or clogs, or some sort of other "Official" footwear. I can't remember ever having seen a pair of sneakers left behind, although I've been known to be wrong about these things.
Other variations on this include small piles of dust being left behind in the boots, important personal effects of the deceased (watch, credit cards, blackjack) landing in the boots after the vaporization, and in the case of Biblical epics, a pair of sandals instead of boots. | 
