Using Your Head

If you ever need to spark revolution among your allies, but don't want to pay the text-messaging fees on your cell phone, or don't feel like using a computer, and you have lots of patience and a few weeks, you could opt for the method of Histiaios, as explained at 5.35 in Herodotus:

ὁ γὰρ Ἱστιαῖος βουλόμενος τῷ Ἀρισταγόρῃ σημῆναι ἀποστῆναι ἄλλως μὲν οὐδαμῶς εἶχε ἀσφαλέως σημῆναι ὥστε φυλασσομένων τῶν ὁδῶν, ὁ δὲ τῶν δούλων τὸν πιστότατον ἀποξυρήσας τὴν κεφαλὴν ἔστιξε καὶ ἀνέμεινε ἀναφῦναι τὰς τρίχας, ὡς δὲ ἀνέφυσαν τάχιστα, ἀπέπεμπε ἐς Μίλητον ἐντειλάμενος αὐτῷ ἄλλο μὲν οὐδέν, ἐπεὰν δὲ ἀπίκηται ἐς Μίλητον, κελεύειν Ἀρισταγόρην ξυρήσαντά μιν τὰς τρίχας κατιδέσθαι ἐς τὴν κεφαλήν.

[For Histiaios, wishing to signal to Aristagoras to revolt, had no other safe way to signal, since the roads were guarded, but, having shaved his most trustworthy of slaves, he marked his head and waited for the hair to grow out, and as soon as it grew out, he sent him to Miletos, having ordered nothing else to him, but that when he should arrive in Miletos, to tell Aristagoras, after shaving his hair, to look at his head.]