The common iconography for Myrmidia would be the blazing sun, the spear or the eagle
Yes, the official religion of the Empire is Sigmar, but in my mind really only the nobility and soldiers would be dedicated followers, ordinary citizens would more likely be praying to Taal, Rhya and Morr, even Ulric more frequently, though they'd ackowledge and pray to each god on their particular holy days. Certain areas of the Empire such as Middenland and the northern states, the soldiers would be as likely to follow Ulric. And since those two cults while not openly hostile, are not exaclty cordial to each other, so I doubt a Knight of the White Wolf would ever have a comet, nor would a Sigmar worshipper have a wolf. Templars to a deity would almost exclusively use their own god's icons, at least in my opinion.
So...Maybe you could convert that comet into something more like a sun? Maybe with a spear tip going through it?
Also, off-topic ish, a particular beef I have. I don't like they way the Arch Lector has been downgraded in the fluff, they seem to be on a par with Grandmasters and Generals and Wizard Lords, when they should be special characters at the level of Elector Counts - there are only two of them Arch Lector Kaslain of Nuln and Arch Lector Aglim of Talabheim, and Imperial Electors in their own right - hence the name Arch Lector, though that impleis there are normal Lectors, of which there are, but If I dig out my WFRP sourcebooks this post could get long. And it does say the The War Altar of Sigmar, not A War Altar of Sigmar.
