N.J. Stat. Ann. § 2A:44-176

Any notice prescribed by this article may be served upon the owner of the watch, clock or jewelry upon which the lien is claimed either personally or by registered mail, with return receipt demanded, directed to the last known address of the owner, or if the owner or his address is unknown, the notice may be posted in 2 public places in the municipality in which the lien claimant conducts his place of business.