Sigils and coats of arms are certainly very popular in America. Besides the practical purposes of distinguishing soldiers on the battlefield in feudal zones, they're just appealing to a country raised on sports teams and advertising mascots.
It should come as no surprise some of the most ubiquitous charges unique to America include the bald eagle, Lady Liberty and the Liberty Bell, and the coonskin cap associated with Davy Crockett. Denizens from America's own bestiary like Bigfoot and Jackelope can also be found.
The Big Four from Game of Thrones are very popular charges, as it became popular in Industrial times to evoke the main Houses from the show, even on generic medieval paraphernalia.
The lion (or "lion", as Americans have largely conflated just about every larger-sized cats) is about as emblematic of a coat of arms beast as you can get, though the the continent doesn't have quite the attachment, due to wanting to distance itself from symbols of monarchy for the first couple of centuries. The stag however, is quintessentially American, associated with everything from hunts to Native American mythology.The wolf was certainly no stranger to European coats of arms, but it saw an upgrade, due to its status as one of the continent's apex predators, that House Stark is among the most sympathetic characters in George Martin's epic, and perhaps most importantly, the animal being the entry level badge for the cub scouts. As a result, it's one of the few heraldic beasts to more often being depicted by just its head.
Dragons are of course, very popular, but the Eastern version is actually more common, perhaps not to have it confused with the Jersey Devil, and because the ruins of Chinese restaurants left more of an impression on generations.
Creatures native to the America are largely the most frequently found, including the bison, the alligator, the raccoon, the bald eagle, and the rattlesnake. Old world animals which are arguably more prominent in America are the moose, the turtle, with bears and owls more or less being as frequent.
In terms of plantlife, the oak and its acorn is common pick, but olives and pomegranates are somewhat rare compared to pines and apples (and for that matter, the pineapple). The Fleur De Lis, with its connections to Quebec, Louisiana, and scouting organizations, will also tend to show up. Of course, the native maples and cacti are frequent charges on the frontiers of the feudal core. Shamrocks aren't unheard of, due to the large Irish ancestry, but mot Irish descended people live in the republics, and not courtly families. New world crops are also common, particularly corn and tobacco.
Speaking of which, some of the man-made items that are fairly new feudal heraldry include the smoking pipe, the tomahawk, and the umbrella. (What a way to show your family is always prepared) It's also not uncommon to use astronomical phenomenon like comets or Saturn's rings. America's temperatures can be a lot more extreme, and depictions of tornadoes and hurricanes are up there with thunderbolts. Finally, it's not unheard of for a family to use musical notes as a sigil--to display culture, and to indicate they descend from someone famous--Elvis or the like.
In terms of symbols from American industrial and popular culture, they're not super frequent, but the Captain America shield can be found in some family or another from just about any major country. The five-pointed star surrounded by three rings will often use the red white and blue to indicate piety by way of the Non-Denominational Church, or may use colors found on the national flag. The Death' Head, reminiscent of the Punisher, is a carryover from its informal popularity with law enforcement. And of course, while the bat is animal found in actual medieval heraldry, the popularity of Batman probably kicked it up a notch.
To a cynic, perhaps nothing symbolizes America like McDonald's, and its relationship to feudalism isn't too far off (Ray Kroc famously franchised the brand by being a landlord, as opposed to claiming the IP). No, knights who use the charge aren't descended from former franchise owners, who used a Mickey D's as fortress, but it does serve as something of latter day version of the Horn of Plenty.