Have the default shell prompt show the server and db names.

So when you are connected it would look like this:

localhost/test>

If the port is non-standard it should included (server:port).

Optionally you could also include other notations for master (m), slave (s), replicaset (rs), mongos (p – for proxy), ...

We could even go as far as this "localhost(p)-server1(m-rs)/test>" to indicate that you are connected through a mongos (proxy) to a replicaset on the current master node (server1) on database test