counter-signaln.
Etymology: counter- prefix 2d: compare French contre-signal, Italian contrasegnale (Florio).Previous versions of the OED give the stress as: ˈcounter-ˌsignal.
1818 H. J. Todd Countersignal, a corresponding signal; a naval term. [Hence in mod. Dicts.]
This entry has not yet been fully updated (first published 1893; most recently modified version published online June 2019).