Igitur rex Theodericus illiteratus erat et sic obtuso sensu, ut in decem annos regni sui quattuor litteras subscriptionis edicti sui discere nullatenus potuisset. de qua re laminam auream iussit interrasilem fieri, quattuor litteras “legi”* habentem; unde si subscribere voluisset, posita lamina super chartam, per eam pennam ducebat, ut subscriptio eius tantum videretur.
(Excerpta Valesiana 79)

Now King Theodoric was without training in letters, and of such dull comprehension that for ten years of his reign he had been wholly unable to learn the four letters necessary for endorsing his edicts. For that reason he had a golden plate with slits made, containing the four letters “legi”*; then, if he wished to endorse anything, he placed the plate over the paper and drew his pen through the slits, so that only this subscription of his was seen.
* “I have read (it).” Or perhaps ΘΕΟΔ.

(tr. John C. Rolfe, with his note)

Ὅπως δὲ μαρτυρίαν τῆς βασιλέως χειρὸς ἔχοιεν, οἷς δὴ ἐπίκειται τὸ ἔργον τοῦτο, ἐπενοήθη τάδε. ξύλῳ εἰργασμένῳ βραχεῖ ἐγκολάψαντες μορφήν τινα γραμμάτων τεττάρων, ἅπερ ἀναγνῶναι τῇ Λατίνων φωνῇ δύναται, γραφίδα τε βαφῇ βάψαντες, ᾗ βασιλεῖς γράφειν εἰώθασιν, ἐνεχειρίζοντο τῷ βασιλεῖ τούτῳ. καὶ τὸ ξύλον, οὗπερ ἐμνήσθην, τῷ βιβλίῳ ἐνθέμενοι, λαβόμενοί τε τῆς βασιλέως χειρὸς, περιῆγον μὲν ξὺν τῇ γραφίδι ἐς τῶν τεττάρων γραμμάτων τὸν τύπον, ἐς πάσας τε τὰς τοῦ ξύλου αὐτὴν περιελίξαντες ἐντομὰς οὕτω δὴ ἀπηλλάσσοντο, τοιαῦτα βασιλέως γράμματα φέροντες.
(Procopius, Anecd. 6.14-16)

But in order to obtain formal ratification by the imperial hand*, those who supervise this matter devised the following scheme. Onto a small strip of polished wood they carved the shape of four letters that spelled, in the Latin language, the word “I have read.” They dipped the pen into the special ink that is used for imperial subscriptions and put it into the hands of this emperor*. Then they placed the slat of wood that I mentioned upon the document and, holding the emperor’s hand, traced the pattern of the four letters with the pen, following the curving lines that were cut into the wood. And so, they would complete their business with the emperor in this way, having obtained his handwritten letters, such as they were. (tr. Anthony Kaldellis)

* Justin I.