Many cruise liners now carry 'Security warning KEEP AWAY XXX METERS' on large banners for all to see. Regardless of the language spoken and any maritime law applicable, in any stretch of water it hopefully reads 'board my vessel and you will fall overboard' Armed only with 'fire hoses' and to make potential threats think twice.
In any language, big and grey and flying any military power flag, you will be fired on if they feel threatened and you do not answer their call.
There are many ways to attract the attention of a warship, VHF or not if you need assistance, they will assist.
Warships, support vessel or Battleships tend to be easy to spot.
Right or wrong, it is a bit like chancing your luck when you hear 'Armed Police' stop running!'