I'm also a bit perplexed because I'm a retiring US federal employee and in addition to the signature issue, that process is now exceedingly slow an unresponsive to questions. I'm going to get a letter from my supervisor on letterhead which seems to meet the TUPA requirement. But if it needs further authentication, I'm not sure if the state will handle a notarized letter from a federal official, or if they'll kick it to the very slow US State Department which may have a question about its validity as a federal document. But I can work that out if needed.
I suppose the usual answer is "try it all", but if they'll accept the simple copy (translated) that would be great!
Thanks for any insight!