What's that strange icon next to login query in PuTTY?

Question

I noticed a weird icon when I logged on from a new computer:

Here's the icon enlarged:

Older version of PuTTY doesn't do that.

Does PuTTY detect login queries and mark them like this? Or does SSH mark the queries with special character which putty renders like this?

Answer 1

Does PuTTY detect login queries and mark them like this?

It doesn't need to detect anything; PuTTY itself generates these particular queries. As of version 0.71, it will show an indicator that marks locally generated lines to avoid confusion with text sent by the (possibly malicious) server.