When traveling abroad, people tend to characterize a persons nationality with stereotypes. Americans are not free from this peril and quite frankly it can be true. We can be loud. We can be obnoxious. We can be ignorant, but almost anyone can be like that.
The biggest worry people fear when going overseas is being judged for those stereotypes, but on all my travels I have yet to be discriminated because of where I come from.
Maybe it is the way I carry myself, maybe it is because we were taught how to conduct ourselves, but so far i have had great experiences with the London locals and hope it continues.