A flashlight might be the only thing you could find that would be "globally acceptable" (and I wouldn't be sure about that).  The only reason a flashlight might be accepted most places is because it's primary function isn't self defense.  Anything actually made for self defense will also be seen as a potential offensive weapon and will be subject to various restrictions, jurisdiction dependent. 

Some less than lethal (well, usually less than lethal) possibilities: OC (pepper) spray; stun guns; impact weapons.

 

A forgotten impact weapon from an earlier era is the sap.  I've never used one, but many old time cops swear by their effectiveness.  Stories abound about some old jail sergeant who knew all the "sweet spots" and could lay out an inmate with a flip of the hand without leaving a mark.  Embellished?  Maybe, but stories like that get started because they have a foundation of truth. 

 

As you might imagine, saps are not legal for the public in many places and even against many LE department's carry policies these days.  They're still sold though, so check before you buy.