How much are aircraft nose paintings restricted by regulations? It's actually surprising to see these old paintings on aircraft noses:


WW2 nose art, source

How much were (and are) these paintings generally restricted or allowed by law, civil regulation and military rules in countries like US, Russia, India, Australia (if the jurisdiction matters for a general answer)?
It used to be that nose art was pretty outlandish and sexually charged, and it remained largely unrestricted as this B-24 from WWII demonstrates.



With the current gender integrated units and women serving in combat squadrons, this kind of stuff is non longer acceptable.  Currently there's a rule, in at least the USAF, that nose art must be 'non-gender specific' i.e. you can't paint naked women on your airplane.