What is the big (about one meter) upside-down “V” (or perhaps an upper-case Greek lambda) often painted on the side of main battle tanks. By ‘tanks’ I mean tracked armored combat vehicles, not fluid storage containers.

This is not just one country’s military marking, I’ve seen it on video of US, Israeli and other nation’s heavy tanks, but never on other military vehicles like APCs or half-tracks.

Googling it yields many conflicting answers, mostly as a badge to avoid friendly fire (why not just a flag or other national symbol, like the white or red star or Iron Cross in WWII?).

Some say that it honors the Greek lambda from the shields of Spartan hoplites (the country Sparta was in was Lacadaemon, which begins with lambda in the Greek alphabet.