Whilst not commonly seen in churches or religious settings, a cross with the Greek ΙΧΘΥΣ (Ichthys) is a popular jewelry item.
A plain cross, without lettering, is one of the most common designs for necklaces, usually worn for decoration only. Adding the Ichthys lettering reminds people of the Christian meaning of the cross.
Ichthys is a Christogram or Chrismon, a monogram of Christ, and was in use by the 4th century if not earlier. A more detailed description is on our Jesus Fish page.
Other Chrismons include INRI, Alpha and Omega, Chi-Rho, ICXC and IHS - all of which are more commonly seen with the cross than Ichthys.
Sean Wright noticed this neat variation of an Everlasting Cross on a magnet sold by CafePress.com (www.cafepress.com/+jesus-fish+magnets).