Laudator Temporis Acti

Augustine, Sermons 306C.1 (tr. Edmund Hill, with his note):

What a splendid wall for wall posters⁴ this Quadratus had presided over!

4. Parietem signinarium. This odd word is not given in Lewis & Short's Latin Dictionary. I am guessing that here it indicates a wall—whitewashed, of course, because it was the White Mass—on which signs, advertisements, can be painted, and graffiti scrawled; it's a novel metaphor for a fervent community of martyrs: a billboard for Christ.

Latin text from Germain Morin, "La Massa candida et le martyr Quadratus d'après deux sermons inédits de S. Augustin," Atti della Pontificia Accademia romana di archeologia (Serie III). Rendiconti, Volume III (1925) 289-312 (at 296, with his note):

Quam magnum parietem signinarium (?)²⁰ regebat iste Quadratus!

²⁰ signinarium] Restitution conjecturale. Le manuscrit a sigmnarium, dont il n'y a rien à faire. Mais l'adjectif signinus est d'usage courant, par ex. «signinum opus» (PLIN. 55, 46, 5): «signini parietes» (PALLAD., 1, 17). On trouve aussi simplement «signinum, signina». La pensée m'est venue qu'Augustin avait pu former de là l'adjectif subsidiaire «signinarius»; le copiste aurait écrit un m au lieu de ni. Mons. Giov. Galbiati, Préfet de l'Ambrosienne, partage en cela ma manière de voir.

Signinarius isn't in Alexander Souter, A Glossary of Later Latin to 600 A.D. (Oxford: Oxford University Press, 1949), either. Cf. Lewis & Short, p. 1696, s.v. Signia: Signinarius occurs as a proper name (or a profession?) in an African inscription — Corpus Inscriptionum Latinarum VIII 1 7462 (CAI IULI SIGNINARI).