Unlike Bitcoin, Nxt presently relies solely on brainwallets as the means of user authentication. There is no "cold storage" alternative offered.
Type anything like
NW948YN3V95YN0PWS93498934N376N095HG857028MEOAWMFYCNOQA789O837QY8
Save it and use as a cold storage passphrase.
The account (16025050820116515852) has 0 coins. Wait a few days and we will probably see something there lol!