I've signed up for icloud storage. How do I know if my photos are on the icloud?

You can then check the status in photos.

Open photos

Tap library

Scroll to the bottom

You'll see the count of items to be synced and the current status.

Remember, iCloud is a synchronization service and not offline storage. Any additions, deletions, or edits will reflect on all devices.

Enable iCloud Photos (settings>photos on an iDevice). On a Mac: Open photos. Go to photos > settings > iCloud