I believe you're correct Matt. I think it's a Christogram, reading 'IHS', as the first three letters for the name Jesus in Greek/transposed to Latin. It's the most common of the Christograms used mainly by Catholics, but increasingly other Christian religions.
Google 'IHS mongram' click on 'images' and look at the many variations.
Incidentally, religious charm medalets worn round the neck which have a 'message' are sometimes intentionally worn 'upside down'. It's so that the wearer sees the message the correct way up when the charm is raised to the face for moments of prayer or contemplation.