Could they use “thumb rules” if said species have thumbs? One that us fleshy puny humans use is the right hand rule where a third axis convention (up) corresponds with counterclockwise movement by the hand curl. Of course you could easily use the other hand since they’re arbitrary anyway.
You’ve stumbled across the answer in your own question. The hand choice is arbitrary, and the direction is a binary choice between the galactic plane looking clockwise or counterclockwise. So you’ll get an even mix of upside-down and upside-up ships when you choose that normal direction arbitrarily.
Could they use “thumb rules” if said species have thumbs? One that us fleshy puny humans use is the right hand rule where a third axis convention (up) corresponds with counterclockwise movement by the hand curl. Of course you could easily use the other hand since they’re arbitrary anyway.
You’ve stumbled across the answer in your own question. The hand choice is arbitrary, and the direction is a binary choice between the galactic plane looking clockwise or counterclockwise. So you’ll get an even mix of upside-down and upside-up ships when you choose that normal direction arbitrarily.