There is no record of the image of Hercules could have on the shield, but then yes, actually in the third century AD, the image of Herculiani sources say was an image of Hercules, and the Joviani, one of Jovius (Zeus).
Later, with Constantine's civil wars, probably end up switching to the black eagle which includes the Notitia, until Julian's re-introduced, and finally put Valente and Valentinian again, and finally, the eagle (as I recall)
Thanks!
Anyway long ago I suggested the same image but nobody paid any...