Adiyen lives in the US and always adorns Thirumannkappu even while going out; some ask what Thirumannkappu is; how do I explain it to them? Some ask whether I belong to ISKCON looking at my Thirumannkappu; how to explain that adiyen is a Srivaishnava and the difference between us and them?

Thirumannkappu is the divine symbol signifying the holy feet of Perumal; we are proud and happy to adorn his symbol as it pleases Emperuman.
Generally, westerners have the tattoo culture, of painting tattoos on their bodies; but nobody seems to question them; even if some question them, they say it suits them and are happy to wear tattoos. If somebody questions us on Thirumannkappu, we shall also reply with pride that we are happy to adorn it as it is for the pleasure of our Lord.
We can clarify that we do not belong to ISKCON and that there are philosophical differences between us Srivaishanava-s and ISKCON; if they are aware of philosophical differences then they would not question us; so it is better to tell them just philosophical differences and leave it at that.