Your character can know and recognize Dream if:
→ They have a talent for dreams, illusions, and/or clairvoyance.
→ They have a particular fixation with his mythology (i.e. Morpheus, the Oneiros, trickster spirits) etc.
What can Dream 'know' about your character? (This can be anything small, from their name or favorite food, to important canon events, recurring nightmares, aspirations, etc.)
When can Dream bring up the above information? (In private comments only, in front of people, over coffee and breakfast, etc.)
Bear in mind that Dream can be rather blunt, and tends to be lacking in a little thing called tact, so feel free to engage in verbal sparring with him any time. If you want things to get physical, well...
I'm certainly open to discussion.