And, IMHO, therein lies the rub. People of the clan who's tartan is being worn will likely recognize it and be curious about the (assumed) kinsman who they have not yet met wearing it. An innocent and friendly inquiry could very likely ensue. It would be good to have an answer for such a question which shows respect for the tartan and to those who hold it in high regard.
Good point. I once spotted an American wearing a Cunningham tartan kilt and as I was also wearing my Cunningham kilt at the time I introduced myself as a Cunningham and he insisted the tartan was Robertson. Nothing could convince him and as far as he was concerned I was just an ignorant Scot who did not know my tartans. I could have gone on and told him that I am a Clan Cunningham Armiger here in Scotland but it seemed pointless to do so. He who knows not and refuses to learn from others is best ignored.