Here’s an interesting article for those interested in Patristics and papyrology: Francesca Schironi, “P.Grenf. 1.5, Origen, and the Scriptorium of Caesarea,” Bulletin of the American Society of Papyrologists 52 (2015): 181-223. The abstract goes as follows:

P.Grenf. 1.5, a fragment from a papyrus codex with Ezekiel 5:12-6:3, is here put in its historical context. Since it was written close to Origen’s own lifetime (185-254 CE), it provides early evidence about how he used critical signs in his editions of the Old Testament. It also sheds light on the work of the scriptorium of Caesarea half a century later.”

Quite interestingly, Francesca Schironi argues that inasmuch as the by-product of Origen’s Hexapla was a stand-alone edition of the LXX ‘enriched’ with Hebrew readings (in which the textual differences were marked with text-critical signs, using obelos to mark what is present in the LXX and not in the HT, and asteriskos to mark what is absent in the LXX but present in the HT), then P.Grenf. 1.5., which contains a fragment of Ezekiel and displays such critical sigla, may well just be a very early remnant of this by-product (or rather end-product?) of the Hexapla, and quite close to Origen’s time.

This is an extensive, well researched interesting article. Other articles on critical signs in the papyri (and a host of other topics) can be found on the author’s academia edu page, here.