At first I thought this reverse inscription read LAETITIA AVGG (with two Gs) but, unsurprisingly, that reverse inscription only occurs with obverse legends used during Gallienus's joint reign with Valerian, such as IMP GALLIENVS AVG, IMP C P LIC GALLIENVS AVG and IMP C P LIC GALLIENVS P F AVG. Moreover, were it to read AVGG, the first of the two Gs would be very strangely rendered. No, the letter between the V and the G in AVG is an officina mark, V (upright), but placed very far in the right field to the right of Laetitia's hand such that it intrudes on the reverse legend. This would have never happened had the reverse legend been engraved before the officina mark was added; the engraver would have placed it above or below Laetitia's hand because the G in AVG would have been to the right of the goddess's hand. This demonstrates that the officina mark was added before the rest of the inscription. I think the sequence of engraving the die was as follows: The figure of Laetitia was engraved first, followed by the placement of the officina mark V in the right field, and lastly, the reverse inscription was added. Gallienus, AD 253-268. Roman billon antoninianus, 3.20 g, 21.6 mm, 6 h. Rome, AD 262-263. Obv: GALLIENVS AVG, radiate and cuirassed bust, right. Rev: LAETITIA AVG, Laetitia standing left, holding wreath and anchor, V in right field. Refs: RIC 226F; Göbl 498q; Cohen/RSC 424; RCV 10250; Hunter 15. Here are a couple of more typical examples (from gallienus.net and Gallienus and family, respectively), where the die-engraver better anticipated the need for the reverse inscription: Again, I welcome any comments or observations. Please feel free to post anything you feel is relevant!
Here's Gallienus with Soli Invicto's horse, or what some call Pegasus, A(?) in field. Great coin @Roman Collector !
Interesting coin and astute observation. Although the officina mark was engraved first on some coins, it doesn't follow that it was always engraved first. For the subsequent examples you show, you say that "the die engraver better anticipated the need for the reverse inscription." For these coins, why do you think that the reverse inscription wasn't engraved first? I don't see any visual evidence for that. For these coins the composition of the reverse doesn't look crowded, which points to the opposite: that the officina mark was engraved after the inscription.