A hechsher (plural: hechsherim) is the visible mark by which a recognised rabbinical authority certifies that a product, including a spirit, complies with the laws of kashrut. It typically takes the form of a stamp or symbol on the bottle's label, accompanied by documentation that names the certifying body.
Common global hechsherim include the OU (Orthodox Union, United States), Star-K (Baltimore), OK Kosher, Kof-K, the KLBD (Kashrut Division, London Beth Din), Manchester Beth Din, the cRc (Chicago Rabbinical Council), MK Kosher (Montreal), and Chabad-Lubavitch rabbinical authorities in their respective jurisdictions.
A hechsher is not a flavour claim. It attests that every input, every piece of contact equipment, every adjunct, and every cleaning protocol in the production has been examined and approved by named rabbinical supervision. For collectors, this is increasingly read as a strict provenance audit, independent of the buyer's religious observance.