If you have a tartan associated with your name or lineage, that would be the obvious and most accepted choice. And while there are no 'tartan police' that will assault you for wearing a tartan to which you have no affiliation, you can at least expect social awkwardness if you do wear it.

For example, if you're at a Highland Games and you're wearing a Cameron tartan (but have no affiliation with the Camerons), you may have people coming up to you who ARE Camerons, wanting to establish the kinship connection. And that's really part of the point of clan tartans... to be an identifier of kinship or affiliation. It can be mighty awkward having to explain to these fellows who were about to adopt you as a long-lost cousin that you're not kin to them, and that you're just wearing their tartan because you got a good deal on it or you like the colors.

Will they beat you up for it? Not very likely. But still, it can be awkward. It's your choice, though.

Personally, I will only wear the clan tartan to which I have a blood connection, as I would rather not identify myself as something I'm not. But there are plenty of organizational and district/region tartans out there too, so it's not like there's only one tartan choice.