AFAIK Uro parts uses the ISO county code, with Thailand being one of the world largest rubber producers with many companies operating pants there it makes sense the rubber part was made there hence the TH.
A lot of their parts are TW =Taiwan. The International vehicle registration code is not applicable, Germany would be DE in the old ISO or DEU in the UN code and only use the D for the vehicle registration code.
Like Dorman the vast majority of their parts are very low quality but once in while they buy and repackage a real gem, its a crap shoot with them. I have seen [D], and a few others on their boxes but it does not seem to have anything to do with COO, some of the stuff marked TW on the box also have Taiwan on the part itself.