Our female Burmese, "Honey" sits like that quite often while grooming away. Sometimes she looks up from grooming when interrupted and we've caught many poses just like yours.

It's adorable- but my wife kiddingly calls her a floosy.

To me, it's a sign of trust.

"Yes, this is my kingdom and I am quite comfortable here. I am capable of being either stately or lowly, depending upon my mood. If you question my purpose or my posture, I'll quickly turn my rear on you! So watch it buster."