In general, the narrower and more misshapen a cork extracted from a bottle, the longer it has been there. This is a particularly useful clue to the likely age of a non-vintage sparkling wine, or at least to the time that has elapsed since disgorgement. It can also provide a clue to the likely age of any other non-vintage wine, or fine wine which has lost its label or, perhaps in the case of vintage port, never had one (although see also recorking).
Most fine wine corks are emblazoned with the name of the wine producer (if not the wine itself) and, often, the vintage. Different countries adopt different conventions. Italian corks, which fit particularly tightly into their narrow bottle-necks, are often marked with a two-letter regional code (UD for Udine on many friuli wine corks, for example). Most British wine bottlers brand their corks with a W followed by their own numerical code. The regular French message is simply mis en bouteille à la propriété.