I used to work for Siemens, there is in fact more of a story for that.
Prior to the SIRIUS line of electro-mechanical components, their contactors and SOME of their other devices were called the "World Series", because Siemens was trying to sell the same parts all over the world, so the design was a compromise of IEC and NEMA concepts, but some of the things they had to do to meet NEMA specs were less than ideal for IEC customers.
After Siemens bought Furnas and incorporated their NEMA design products to serve North America, they decided to change their IEC product lines to focus more on the European market, because Schneider and ABB were eating into their market share. So they wanted a new name for the new product lines. Sirus, the "Dog Star", is associated with an old European myth going back to the Roman times, when it was called "Custos Europae", meaning "Protector of Europe". That, plus the fact that it started with "SI" and fit in with their SIMATIC branding trend, is why they chose that name.