Other campaigns in the past, both Republican and Democratic, have done similar things.
Links?
I hear you Mike, as does almost every single cardboard yard sign for a Federal office election you care to see...
But re-working the seal of the office of the POTUS like that is creepy. Sorry, it just is. While the flag has proper display standards, it's parts and colors have also become an ubiquitous representation for all things "Americana", such that the use of the red white and blue, and stars can be stretched pretty far.
But the American Eagle with the arrows and olive branches and the shield is a very specific thing.
I know it was unintentional, and I don't really read much into it, but making up their own seal like that, it conveys a very specific impression well beyond simply plastering stars and stripes on something.