Mystery mark on slip glazed tankard - Swiss? Eastern European?

A hand thrown red clay tankard with slip decoration. An incised mark on base edge ‘KTO’? Anyone recognise? Thanks

Looks like one of the Swiss Thoune potteries

Thanks for that. I've had a look and not found it. The body is a very dark reddish brown. The glaze has a matt lustre, not gloss. Obviously a 'folk' feel to it, maybe East European? Maybe has some age too.