It's a very familiar style, like recognising an unsigned letter/message from someone you know well because it 'sounds like them'. Not really so much a deterministic list of things that make it Claude (if it were so, fixing it would be easy) but if you insist 'One caveat with that fix:' abrupt introduction/call to attention immediately sounds like it to me. Steps through it in concise detail, and then 'Worth checking' summary somewhat stating the obvious, with a curiously vague 'if the source publishes one'.

The "Worth" at the end clues it in for me. The rest seems a little clipped, but that "Worth" at the start of a sentence is painful. Most people would say "It's worth" instead.

Of course, I've now helped Anthropic fix that and make it harder to detect, but oh well.

nothing ... Worth ...