Unless one has grown up with it, I cannot see that the intent of "dead end" on a road sign is at all obvious. The oft-used alternative "no outlet" at least means what it says. And while a non-native English speaker might have difficulty with "no outlet" I suspect that it could be looked up in an English-to-x dictionary, but "dead end"? I think not. So why did "dead end" come to mean that the end of a road is imminent?
closed as general reference by Mark Beadles, Gnawme, cornbread ninja 麵包忍者, Mahnax, Matt Эллен Aug 28 '12 at 9:37
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OED 1 s.v. Dead D.2. gives a first citation of the phrase in 1886, with respect to closed water pipes, and in 1889 with a sense approximating the ordinary modern use: "G. Findlay Eng.Railway 199 This is what is termed a 'dead-end' warehouse .. the waggons come in and go out the same way, and cannot be taken through the warehouse."
The definition offered here is "a closed end of a water-pipe, passage, etc., through which there is no way." This evidently derives from ibid. "IV. Without motion (relatively or absolutely)".
I trust that the metaphorical extension of dead is obvious. We speak of dead air, dead water, dead calm, a dead stop; a wire is live if it carries a current, dead if it does not. The dead center of a rotating object is the axis point about which it revolves, at which there is no motion. Dead weight is the weight of an inert, i.e. unmoving body. A deadlock is a struggle in which neither party can 'move' the other.
So a dead end street is one through which traffic cannot move.
The term 'dead-end' may have originated during the time of ancient Rome in which streets were planned for defense purposes. If an enemy entered a 'dead-end' street, they would be trapped with no escape, and would be easy targets for defending troops. Leon Battista Alberti writes during the 15th century that
See Leon Battista Alberti, Ten Books on Architecture, 1485, ed. James Rykwert(New York: Transatlantic Arts, 1966) Book IV, Ch. V. 75 cited on Wikipedia.