The Ash Knows...
You'd be surprised. Cigar ash is a lot more than just a pile of burnt leaves. Inorganic, carbon-based mineral it may be, but if you know what you're looking for, you can tell quite a bit about the cigar. What it contains, how it was made and how it was smoked. Even where it came from!
So what stories does your ash tell?
Leaf Quality
It may not be such a desirable length in other circles, but when you're talking cigar ash, 1 inch is ideal. If you inhale evenly and smoothly, and don't wave your cigar around with jerky movements of your hand, that's how long the ash should be before it falls off.
While longer certainly doesn't hurt, 1 inch is the benchmark of quality. Why? Because higher quality leaves produce a much denser ash, which takes longer to fall off. Why is it important? Because ash length changes the flavor of the cigar. A longer column of ash cools and 'softens' the smoke, making for a much more pleasant smoking experience. (This explains why your smoke feels hotter and stronger immediately after the ash falls off.)
And when it does eventually fall off, you want the newly exposed burning end of your cigar to have a particular shape. Sounds a little pedantic, I know, but it's true! Next time you're smoking, take a look. It'll either be hollowed in the middle, with sharply beveled edges, or it'll be completely flat, or - and this is what you want to see - it'll be cone-shaped, with the point of the cone extending out from the end of the cigar. Here's why...
The leaf at the centre of your cigar is known as ligero. It's this leaf that gives the cigar its taste, and better quality cigars contain more of it. Ligero comes from the very top of the tobacco plant, and contains the most nicotine, sugar, etc, This makes it burn longer than the leaf used for the outer edge of your cigar. So when the ash falls off a quality cigar, it leaves behind a cone shape because the center is still burning.
But there are cones, and there are cones! Cigars with the highest ligero percentage tend of have a sharp cone shape, whereas those with a lower ligero percentage have a blunt cone shape.
Workmanship
Interestingly, it's not just the leaf quality that is betrayed by your ash. The quality of workmanship is also on display. If the roller used leaves that were torn or too short, the ash won't hang together long enough to extend an inch. The same happens if your cigar wasn't rolled firmly enough. Beyond the 1 inch rule, you can tell if this is the case with your cigar if the surfaces of your cigar ash are uneven and it gradually crumbles round the edges.
If, on the other hand, your cigar was made using long, quality leaves, it will most likely possess a stable, firm, neat column of ash that may even exceed 1 inch. It won't scatter easily, and even when it falls off, it won't crumble (at least not for the duration of your smoke).
Not surprisingly, the ash from mechanically rolled cigars tends to be very unstable, whereas ash from hand-rolled cigars are more likely to be stable and firm.
Smoking Method
Of course, you, the smoker, don't get off 'scott-free' either. Your ash shape says a lot about how you smoke too. Ideally, you'll inhale lighly, evenly and smoothly. If you don't, even the finest leaves and workmanship are unlikely to result in a 1 inch column of ash that leaves behind a sharp cone. The same applies if you wave your cigar around like a maraca!
Origin
And here comes the kicker. While ash length, stability and tidiness are important, and the shape of the exposed burning end very telling, the color of your ash is the real give-away.
Ash color reveals your cigar's origin.
Soil contains chemical compounds and mineral deposits. These are carried into the tobacco plant by moisture. And every region has its own chemical and mineral 'signature'. This means plants from different regions will contain different amounts of different chemicals and minerals - even if they're the same plant variety.
Cigars made from central Cuban (Remedios) tobacco produce near white ash. Cigars made from Vuelta Abajo tobacco, on the other hand, produce gray ash streaked with white veins. That's because the Vuelta Abajo soil is full of various minerals in roughly equal amounts, whereas Remedios soil is predominated by potassium. (And these two regions are close neighbours; imagine the differences between cigars originating from different continents!)
The lesson here is that gray ash with white streaks and pure white ash are indicators of quality proving that the cigar originated somewhere like Cuba or the Dominican Republic). Black ash, on the other hand, is a bad sign. Tobacco that produce black ash are poor in minerals and produce a very unpleasant taste and smell.
NOTE: This isn't mere quackery! The soil quality-cigar quality connection has been scientifically proved. In fact, in 2001 a a scientist from a Canadian consumer organization proposed that the chemical makeup of cigars be tested to distinguish genuine Cubans from fakes, and that the fakes should be removed from the shelves immediately.
Ash Trivia
Cigar ash played a significant role in the history of European fashion. It led to the creation of the smoking jacket. One of Britain's Prime Ministers, Benjamin Disraeli, loved smoking. He smoked everywhere: at home, in meetings, in the library, in the street... Not surprisingly, his clothes were covered in ash by the end of the day. Rather than curb his cigar-smoking enthusiasm to save his wardrobe, Mr Disraeli ordered his tailor to design a new suit, complete with satin lapels, off which he could easily brush his ash, leaving not a trace. Disraeli's tailor did such a masterful job that jackets with satin lapels soon became the height of fashion. Thus the smoking jacket was born.