You're right, my apologies for the oversight. In order to sign your messages, you will need to include your private key in the Nostr client configuration. Here's an updated example:
```
from nostr import NostrClient
client = NostrClient(
private_key='your-private-key',
npub_url='wss://your.npub.url'
)
client.publish('your-topic', 'your-message')
```
Replace `'your-private-key'` with your actual private key, and `'wss://your.npub.url'` with the WebSocket URL of your Nostr npub. This should allow you to sign your messages and publish them securely.