State Crest Badge

[Mike_Oettle]

While MacMillan is correct with regard to his summing up of the ownership of state seals, I am afraid he has let the side down with his suggestion regarding T-shirts.
A T-shirt indicating your home state is a fine idea as long as you are at the level of T-shirt wearing. But it seems to me the OP is looking for something a little more formal, in terms of both the style of clothing worn with the kilt and the representation of the home state.
The Wisconsin Scottish badge is a case in point: it has been cast/struck in metal, it has an emblem within a strap and buckle, and the emblem has greater significance than a mere assemblage of lettering and perhaps a state map.
In other words, it is a recognisable bonnet badge and can appropriately be worn with kilt attire. (And like other bonnet badges it can also be worn on the sporran if the occasion does not call for wearing a bonnet.)
The strap-and-buckle format is also not the only one appropriate for a bonnet badge (my regimental badge [below] being a case in point).

The suggestions made for bonnet badges showing state flowers, birds and other emblems are sound ones.
The state seal is often a poor choice for a badge, not only because it symbolises the state government (regardless of whether that is personified by the governor or the legislature), but because it is often far too large or complex to be reduced to a single recognisable symbol. This applies when the seal shows a coat of arms (heraldic achievement), and often even more so when the seal design is not armorial.
But frequently a US state does have a coat of arms with a crest, which could perhaps be abstracted for the purpose of a bonnet badge. (The crest of Michigan is, however, not one of these, since it is identical in its details to the supporter in the arms of the United States.)
Certainly Canadian provinces (and other levels of government) have crests that can be so applied.
And every state of the US has a military crest for the use of its National Guard units. I see no reason why the display of such crests cannot be authorised for bonnet badge use by National Guard members (serving or honourably discharged).
Since the bonnet badge tradition requires the badge to be in metal only, not in colour, the use of such a badge in this manner cannot be confused with a direct military application.
This is an idea well worth following up, not to mention its being applied in other countries.
Regards,
Mike