Weird temperature settings on heater

I've got one of those heaters on my grow out tank. Those wierd symbols had me stumped too but they are actually the numbers. It just looks like they've been cut in half.

My Hydor-Theo tube heater 'almost' has temperature numbers printed on the adjustment knob, 'almost'. In practical terms the printed temperature numbers weren't all that accurate anyhow - I wound up just tweaking the knob to arrive at the temperature reading I wanted based on a 'stick-on' liquid crystal tank thermometer. Once set in the correct position my Hydor-Theo PTC heater does a great job of holding a stable temperature, but the actual temperature vs the printed knob numbers are off by 3 degrees or so.