I have no idea about this seal. The obverse
has some questions as well: there's a cross
in the middle, in stead of the expected theta. Could also be a letter phi. Also, the delta above is another letter I can't explain.
The last line would seem to be his
command. I could not think of any likely solution. Could be unpublished of course. CVPIAC maybe? Could not find this attested though. Known commands starting with S do not fit (Samos, Seleukia, Sardinia, tou stolou).