Is it riffing off ranch dressing? I've heard that ranch is associated with the US, outside of the US.
Edit: looks like "american sauce" can refer to a multitude of things. Typically it seems to either be some kind of ranch or thousand island.[1] Both of which are separate from "Sauce Americaine", from French cuisine.[2]
2nd edit: If the OP is talking specifically about Heinz brand "American Sauce", apparently the closest match in American cuisine is either thousand island or big mac sauce/"secret sauce" used on burgers (which is based on thousand island). It is pretty American, come to think of it.
Digging a little deeper it appears like McDonalds may have actually invented the sauce to appeal to the Dutch market, where fritessaus is popular (instead of tomato ketchup). Because McDonalds is American, their take on fritessaus grew into it's own thing called "American Fritessaus," or simply "American Saus."
Interestingly, Fry Sauce[0] is near ubiquitous in Utah (and no other US state as far as I know). You can find it on offer just about anywhere in Utah that sells fries.
