Sentence:  In their suburban cottage the crown charges , the Krogers received secrets from the mystery man , usually on the first Saturday evening of each month , and spent much of the week-end getting the secrets off to Moscow , either on a powerful transmitter buried under the kitchen floor or as dots <WSD>posted</WSD> over period marks in used books . 
Meaning of the word marked with <WSD> tags:  affix in a public place or for public notice