watch markn.Nautical a mark worn on the sleeve, indicating the watch to which the wearer belongs.
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society > armed hostility > hostilities at sea > administration and ceremonial > [noun] > naval insignia
swab1793
weekly accounts1805
watch mark1860
killick1915
1860 H. StuartNovice's or Young Seaman's Catech. (rev. ed.) 83 It is now a general rule throughout the navy to have ‘watch marks’ on the sleeve of the frock.