Hi Merenz,
Kudos on you $ idea - I'd rather have got it wrong but have received a special mention from the puzzle's creator for an "ingenious suggestion" :-)
I'm sure you and Loge are correct that "Pentero" is nowhere near cryptic enough, but I'm just at the "consider any theory no matter how unlikely" stage - I'm currently wondering if it might be in some sort of code, a "dot dot dash" or Playfair type thing, but,so far, not a Charles in sight:-(