I've seen them referred to as faction shields on other sites but I've always gone with faction symbols.
Doh my stupid fingers again! I knew it was I N S I G N I A. You know how it is when your typing fast and your fingers don't corporate. Will the moderators please kindly fix it and add emblems to the option? Thanks! And I forgot about logo's, but your right. They are more letters than graphics. I still don't see emblems there though and it won't let me edit the poll section where I made the typo.
Rodimus Prime calls it a symbol in Forever Is a Long Time Coming. A3 and Beta call it the slave brand.
I think the slave brand was only referred to the Autobot symbol. Never heard the Decepticon symbol referred to as such as they were military.
Most of the time I call it symbol. But that's because usually when I say insignia they're like 'What?' but I prefer insignia.