Does anyone actually know how Dutch business men would have interpreted Leviticus? I mean, did Calvin say something about tattoos ? Certainly those men would have enjoyed a pork dinner, which is prohibited in Leviticus. Possibly having a discreet tattoo would be a reflection of your freedom in Christ.
To me that doesn't look very much like a comet. It might be a sword, or a key, or even a nail -- given it's location, possibly identifying with the nail prints of Christ.