Just include your country (or just "I am not an American") explicitly in your question.

Trust me, it used to be much worse ten or more years ago. I remember people switching into panic mode after discovering that someone in their virtual environment didn't share all their cultural background. (I guess it felt like if you went to your high-school reunion, and suddenly some quiet guy in the corner takes a mask off their face and you see a strange brown man with a long beard looking dangerously in your eyes and screaming: Allahu Akbar!) And I don't blame them... the prior probabilities were on their side. More precisely, the prior probabilities of a random English-speaking person on internet not being an American were slowly changing and they still used a version from five or ten years ago when they developed their internet habits. The internet didn't feel like an "outside" place for them.

These days they may assume you are an American, but if you correct them, you won't become the topic of the week. :D

Ten years in the future maybe we will read complaints about people assuming that someone is from outside of India.