Extended Strong's Greek Lexicon (Abbott-Smith based)
an agreed signal
Usage: σύσ-σημον (T, συν-), -ου, τό (σῆμα), [in LXX: Jdg.20:38, 40 (מַשְׂאֵת), Isa.5:26 49:22 62:10 (נֵס) * ;] a fixed sign or signal: Mrk.14:44. (Strab., Plut., al.; condemned by Atticists, see Rutherford, NPhr., 492 f.) † (AS)